Geology and the Art of Birger Sandzén

The following text was written collaboratively by James Welsh, Associate Professor and Chair of the Department of Geology at Gustavus Adolphus College, and Donald Myers, Director of the Hillstrom Museum of Art and Instructor in the Department of Art and Art History. It was produced as part of a recurring exhibit program of the Hillstrom Museum of Art titled FOCUS IN/ON, in which individual works in the Hillstrom Collection are explored in depth in a collaborative process that engages the expertise of College community members across the curriculum and co-curriculum. The text was featured in the Museum’s exhibition FOCUS IN/ON: Birger Sandzén’s Dry Creek Bed, Kansas, on view from September 14 through November 8, 2009, in which was displayed a 1912 oil painting by Swedish-American artist Birger Sandzén (1871-1954), a gift to the Museum from Reverend Richard L. Hillstrom in 2000. This work, which depicts a portion of Wild Horse Creek in Graham County, Kansas, near the home of the artist’s in-laws Erik and Charlotte Leksell, was the impetus for the study, which considers Sandzén, his work, style and career, and his interest in the geological features of his adopted home state, where he lived from 1894 until his death in 1954. The exhibition was presented in conjunction with the 2009 Nobel Conference of Gustavus Adolphus College, titled “H2O: Uncertain Resource.”


Dry Creek Bed, Kansas

Birger Sandzén (1871-1954), a Swedish-born artist who spent his whole career in Lindsborg, Kansas, to which he emigrated in 1894, is known for his images of Kansas and areas farther west such as Colorado and New Mexico. Although he painted portraits occasionally and was also fond of still lifes, especially floral ones of the Kansas sunflower, the large majority of his many works were landscapes that, devoid of much or any human presence, concentrated on the natural formations of the Midwestern and Western topography.

Sandzén was highly prolific, producing 330 different prints of various media, hundreds of watercolors, countless drawings, including 500 large ones he destroyed when they were no longer useful and 5655 sketches in the 83 sketchbooks he left behind, and at least 2890 oil paintings. Many of those works depict scenery from the artist’s adopted state, including the Hillstrom Museum of Art’s 1912 oil painting Dry Creek Bed, Kansas, the subject of this FOCUS IN/ON project. Perhaps as many as fifty-five percent of Sandzén’s landscapes are Kansas imagery, and it is clear that he developed a deep fondness for the gentle plains, rolling hills, low bluffs, and stream beds of the state, even after he began summering in Colorado and painting more dramatic scenes like the Rocky Mountains or, occasionally, the Grand Canyon.

The artist, who spent a great deal of time out of doors as a youth, believed his love of nature and interest in understanding its scenery was related to his Swedish background, according to recollections of his daughter Margaret Sandzén Greenough, in her unpublished manuscript about her father and his work that is held by the Birger Sandzén Memorial Art Gallery in Lindsborg, Kansas. Sandzén thought that worship of nature was a part of his Nordic heritage, and when he left Sweden for Kansas, his interest in the natural setting was transferred to his new home.

Sandzén's Early Life and Training

He had been born in Blidsberg, in Västergötland, a province in southwestern Sweden. His father Johan, a theologian and pastor in the church, was talented as a violinist and poet. His mother Clara had been interested from her youth in drawing and painting. The Sandzéns provided a cultured household, and their son, the youngest of three, had his first formal art instruction when he was nine years old. This was with Gustaf Lundblad, an artist and assistant minister working with Johan in the parish of Järpås, to which the family transferred in 1877. When Sandzén was ten, he enrolled in the Skara Läroverk, a residential school in the nearby cathedral town of Skara, where his older brothers Carl and Gustaf were already studying. There his artistic development continued under Olof Erlandsson (1845-1916), a dedicated instructor who instilled in Sandzén the importance of drawing as a basis for other forms of art. After several years working together, Erlandsson suggested that Sandzén also study painting, which he eagerly began in 1887.

Although Sandzén was devoted to his art studies, he was also strong in other subjects. He excelled in science, and was one of very few students to earn the highest grade in the daunting botany studies, which required identifying 1000 different plants from the collection of samples held at Skara. A certain scientific mindset was to be found in Sandzén, evident not only in his dedicated botanical studies, but also in the butterfly collection he kept, and in the many pebbles and rocks he began to collect at an early age. He had a spirit of inquiry, one that clearly informed—though did not determine—his approach to art.

It is not surprising, therefore, that Sandzén was from early on interested in understanding the geology of the landscapes that would typify his maturity as an artist, even though he abhorred the thought that artworks should serve as topographical illustrations of particular places. In one of his many writings about art, a 1915 article titled “The Southwest as a Sketching Ground,” he warned, “I hope nobody will suspect me of recommending view-painting, since we have already had an overdose of advanced geography in our art.…” Sandzén believed that art was to be an inspired and personal response of the artist to his subject matter, not a transcription of nature. He felt that while it was essential for the landscape artist to grasp the structure of the topography that inspired him, that was not the most important aspect of his work. The artist had the right and duty to speak in his own aesthetic language, and did not necessarily need to adhere to the scientific truth of the subject at hand.

Nevertheless, scientific knowledge of geological subjects that Sandzén portrayed was important to him. And this attitude was born and nurtured in the early years of his education, including when he was asked by the teacher of his geology course at Skara to make enlarged brush and ink images of rock formations for the class.

After he finished at Skara in 1890, Sandzén’s formal education continued at the acclaimed Lund University, where he attended lectures in the history of art and studied French, another subject at which he excelled. He seems to have enrolled at the University intending to pursue an academic career in a subject other than art, but recognizing his strong desire to become an artist, he quit Lund after a single semester and headed to Stockholm with the goal of earning admission to the Royal Academy of Art. Since there was a long waiting list for entrance to the Academy, Sandzén’s strategy was to first study at the Tekniska Skolan, or Technical School, which often served as a stepping-stone to the more prestigious Academy.

Before any openings at the Academy occurred, Sandzén learned that famous Swedish artist Anders Zorn (1862-1920) was planning to start an alternative art school. In 1891, he began study at Zorn’s new institution, one of eight initial pupils at what later became the anti-academic Konstnärsförbundet (Artists’ League) of Stockholm. He often painted five hours each day in Zorn’s atelier, learning important lessons that included the master’s loose handling of paint, an approach that Sandzén soon adopted. He considered Zorn to be brilliant and, although Sandzén’s palette developed into a much lighter-colored, higher-keyed tonality, Zorn’s emphasis on the significance of color was crucial for him. It must have pleased him a great deal when his teacher expressed admiration for his handling and understanding of color.

Following his studies at Zorn’s school, Sandzén left Stockholm to study in Paris, then the most vital art center of the world. He studied with Edmond-François Aman-Jean (1860-1935), a painter connected with Impressionism who had for a time shared a studio with Pointillist painter Georges Seurat (1859-1891). The association with Aman-Jean had a lasting impact on Sandzén’s style and handling of color, especially during a period in the first decade of the twentieth century when he worked in a distinctly pointillist manner, applying his paint in small points or blobs that the viewer’s eye blended together to form a vibrant image.

Sandzén’s period in Paris was brief. While there, he became acquainted with several American art students, piquing an interest in the possibility of moving to America. Sandzén’s father had met Carl A. Swensson, president and founder of Bethany College, originally known as Bethany Academy, of Lindsborg, Kansas. Swensson’s book I Sverige, about his travels in Sweden and the U.S., was read by Sandzén and other members of his family, and it, too, enticed Sandzén to emigrate. In February 1894, he wrote Swensson to offer his services as an instructor at the College. Although Sandzén described himself in his letter as an artist, he indicated that he could teach French and Swedish, in addition to drawing and painting. He must have recognized that a school like Bethany would likely have more need for language instructors than for art teachers, and perhaps he knew that there was already an art instructor there.

Whatever subject he imagined he might teach, were his offer accepted, Sandzén certainly intended to continue developing as an artist. In letters to his father, he discussed at length the effects the possible move to Kansas might have on becoming an artist. Not only was he excited about America, and had been since boyhood when he pored over stories of Indians and the West, but also he felt that his interest in art would only increase in America, and that his prospects for artistic progress in a remote place like Kansas would actually be better for a person of his temperament than an art center like Paris or Stockholm.

To Kansas

Sandzén came to America expecting to stay for only two years, but his residency in Lindsborg extended for the remainder of his life, and he served on the Bethany faculty until his retirement in 1946. This longevity had much to do with the artist’s sense of loyalty to his new institution, and was also related to the presence in Kansas of Alfrida Leksell, whom he met at Bethany only a few days after his arrival and whom he married in 1900. Sandzén returned to Sweden three times for visits, but never moved back to his native country.

He also never accepted offers of teaching positions from the numerous other schools that tried to tempt him away from Bethany. One of these was Gustavus Adolphus College, in 1902 or 1903, and while Sandzén never taught at Gustavus, he had a direct impact on its art program because one of his pupils, Lorena Daeschner Hall, in 1938 became the College’s first art instructor. In 1941, Hall brought her former mentor to campus for a lecture and exhibition, and a number of other works by Sandzén in the Museum’s collection came to Gustavus as a result of that visit, including two additional oil paintings besides Dry Creek Bed, Kansas.

Soon after arriving from Sweden in 1894, Sandzén began traversing the countryside around Lindsborg on sketching trips, which became the inspiration for many of his paintings and prints. Sandzén was devoted to the state’s scenery, both near Lindsborg and farther west in Graham County, around the farm acquired in 1906 by his in-laws, Erik and Charlotte Leksell. His interest in Kansas’ relatively gentle topography did not diminish after he became acquainted with more spectacular locations like the Rockies, and it should not be thought that his preference was for other states like Colorado. In his 1915 article “The Southwest as a Sketching Ground,” he praised the picturesque qualities of the rolling prairies, shallow ravines, and creek beds of Kansas, writing that he considered such features to be “an ideal sketching ground.”

Dry Creek Bed, Kansas and Sandzén's Style and Approach

Dry Creek Bed, Kansas is one of Sandzén’s many works relating to Wild Horse Creek in Graham County, a portion of which ran through the Leksell farm. He would follow the creek sometimes for hours, often setting up chair and easel to produce his many sketches of it. He depicted it very low in water in the Hillstrom painting, and there exist a number of other works in which he also showed it in this dry condition. One of these was a 1916 lithograph Dry Creek, one of Sandzén’s first prints, which is quite similar to the Hillstrom oil. There are also related sketches, including blue pencil drawings in his fifteenth sketchbook, held by the Sandzén Memorial Gallery. One of the thirty-seven sketches in that book—which dates from 1912 and which Sandzén labeled on its cover “Creek Pictures”—is a drawing inscribed with the date July 28, 1912. Given its remarkable similarity to the Hillstrom painting, it is apparent that the latter must be based on it and, therefore, date from between the end of July and December of 1912, the date inscribed in the painting’s lower right corner.

Dry Creek Bed, Kansas was purchased by Museum namesake Reverend Richard L. Hillstrom in Chicago in 1943, from the widow of another prominent Swedish-American artist, Charles Hallberg (1855-1940). Hallberg helped organize a series of exhibitions held at the Swedish Club in Chicago starting in 1911, at which he and his friend Sandzén were frequent exhibitors. For the 1912 exhibit, Sandzén showed five paintings, including one titled The Sentinels that won the second place prize for oil painting, and another titled Dry Creek, which was purchased by Preston Harrison, who, like his brother, Mayor of Chicago Carter Harrison, was a devoted supporter of artists and museums. It is tempting to imagine that the Hillstrom painting could have been the same one purchased by Harrison, except for the fact that the Chicago exhibition took place in March that year, a few months before its apparent date in July or later. Harrison’s painting must have been another of the numerous works representing dry creeks by Sandzén.

The Hillstrom painting dates from the beginning of the artist’s mature style, which is characterized by a vigorous, expressionistic, painterly approach. Sandzén has frequently been compared to Vincent van Gogh (1853-1890) because of his thickly applied, expressively handled paint. Although he noted that he had not, in fact, been influenced by the older artist—whose work he claimed he never saw in person until he was in his fifties—the comparison is apt, and the vigor of Van Gogh is also to be seen in Sandzén.

His coloring is, along with the heavy impasto of his paint, the most characteristic quality of Sandzén’s work. His earlier paintings, especially from Sweden, tended to follow the darker palette of his teacher Zorn, but later he developed a highly personal, brighter approach that, while relating to Impressionism, is more a reflection of the artist’s personal choices. Sandzén wrote about his delight in the bright atmosphere of Kansas and the West, which was very different from his native Sweden. He noted that after he arrived in Kansas, he realized that it demanded a particular palette, citing the clear air that made everything seem more intensely colored. Except for his period as a student, he rarely if ever used black. And he preferred pure colors with minimal mixing, since he felt that too much blending made for a muddied effect, and that greater vibrancy was achieved by juxtaposing rich colors with other rich colors, much in the same way that the Impressionists and also the Pointillists had done.

Sandzén, furthermore, felt that color was crucial in the artist’s creation of structure, which he thought needed to be built up from the start with color, instead of the frequent practice of shaping forms monochromatically and adding hues over top. Many of his pencil sketches were annotated with color indications for guidance in the paintings derived from them. In his 1915 article “The Technique of Painting,” Sandzén stated his belief that the weak point in Western art of his period was its color treatment, later pleading, “…let us experiment and learn to know the joy of orchestral color.” His daughter, noting that other painters of his era such as Regionalists worked with colors that were less brilliant, once asked if he might consider toning down his works and letting the dust of the landscape be seen. Sandzén’s reply was that it would soon rain and the colors would again return to their brilliance. He also told Margaret, “Painting is mainly color expression, although other elements are necessary, such as form and composition, harmony and contrast.” And he told her that if he were to choose just one painter from recent times who could rank with the great masters of the past, it would be French Impressionist Pierre-Auguste Renoir (1841-1919)—an artist known especially for his bright and cheerful colors.

Sandzén and Geology

Both the color and brushwork in the Hillstrom painting are characteristic of Sandzén’s work in general, even if the tonality is somewhat less intense than he often later would paint. And his interest in geological formations is certainly evident in Dry Creek Bed, Kansas, and was to remain a fundamental part of his art, whether he was considering the relatively subtle swellings of the countryside in Kansas or the dramatic formations in the western mountains.

Sandzén had a deep interest in rocks, dating back to his childhood, both for their aesthetic qualities and as a part of his scientific interest. His brother Gustaf once faulted him for all the rocks he had collected, a boyhood habit that continued throughout his life. His daughter recounted Sandzén’s pleasure in finding and examining small stones, and his appreciative comments on their shapes and wonderful colors. She stated that he was “mad about rocks,” while her mother Frida noted, “I think there is nothing Papa gets so excited about as stones.” Sandzén had many of his treasured rocks set into rings, a collection of which are at the Sandzén Memorial Gallery, and sometimes he would allow others to make rings using his stones and trade them for his artworks.

He was equally interested in stone formations in the landscape. Among his drawings from Sweden are studies of Iron Age megalithic dolmen tombs found there, which emphasize the heavy stone material. He habitually sought out monoliths of idiosyncratic character, including in an early painting when he was still in Sweden, a depiction of the ridge at Kinnekulle, a geological landmark where fossils are often found, not far from Sandzén’s school town of Skara. In Kansas, the artist returned again and again to particular geological subjects, including a favorite yellowish rock, with green lichen, located on the slopes of Salemsborg Hills, not far from Lindsborg. Sandzén often took art students to nearby Coronado Heights, a prominent, isolated hill rising 300 feet above the surrounding area that has distinct geological layers of gray and red shale topped with Dakota Sandstone. And he sketched in detail the peculiar, large rock formations at Mushroom Rock State Park, not far from Lindsborg, which were formed by differing erosion rates of a “stem” made of softer, sedimentary layers, topped by a larger “mushroom cap” of harder, more resistant stone.

Although Sandzén did not formally study geology, it was of interest to him, and it was a subject that was emphasized at Bethany in its early years. The first teacher at the College, Johan A. Udden, was a geologist who became prominent in the field. He left Bethany before Sandzén’s arrival, however, teaching for many years thereafter at Augustana College in Rock Island, Illinois, but prior to his departure, he worked on geological field studies in the area. A colleague who had collaborated with Udden, John E. Welin, was Professor of Natural History and Geology at Bethany when Sandzén arrived in 1894. At that time, Bethany students studied mineralogy in their junior year and geology in their senior year. Sandzén was on friendly terms with Welin, and must have had many opportunities to discuss geology and his interest in rocks with him. Sandzén also developed a friendship with prominent geologist Fritioff M. Fryxell, a noted expert on the Grand Teton Mountains who taught at Augustana College. He and the artist made hiking trips into the Rocky Mountains around Estes Park, Colorado, where Sandzén spent many of his summers in the late 1920s and 1930s, and they doubtless discussed at some length the geology of the area. Fryxell was an advocate for landscape painters and, as a result of his promotion of Sandzén, there are several works by the artist in the collection of the Augustana College Art Museum.

Sandzén’s fascination with geology is apparent in much of his work, including the Hillstrom painting. The artist recalled spending hours wandering in creek beds like the one in Graham County near the farm of his wife’s parents, about which he told his daughter, “Wild Horse Creek was a blessing to me and a lesson in simple construction…of earth, of ground itself. Water, sandstone, hills, and pasture—just the kind of landscape that gives one a lesson in mother earth….” Sandzén must have also been interested in the changing seasonal water levels, and while Dry Creek Bed, Kansas is based on a time when the creek was very dry, he would have also seen it in wetter conditions, pondering the effects of water on the formation of the landscape. His 1921 oil painting Creek at Moonrise, in the Brooklyn Museum of Art, shows the creek fairly full of water. Sandzén’s article “The Southwest as a Sketching Ground” contains the following passage concerning Kansas' creeks: “Perhaps a creek will cut a deep gash in the undulating prairie. Sometimes it is full of water, sometimes it is almost dry, and its bottom of sand or shale is laid bare for many miles, except in the deep places, where there is water even in the driest summer.”

Water and Dry Creek Bed, Kansas

Water is, of course, of fundamental importance not only in shaping the land but also in sustaining life on earth, and the current state of world water resources is under consideration at the 2010 annual Nobel Conference of Gustavus Adolphus College, titled “H2O: Uncertain Resource.” In conjunction with this theme, two important points of geological interest can be made about Dry Creek Bed, Kansas.

First, this painting of a Great Plains landscape dissected by a creek valley depicts the fundamental geologic theme of “change through time,” highlighting the role that water plays in sculpting the landscape. It is water that obviously has cut the valley shown in Sandzén’s painting, and it is water that carried the sediment from the juvenile Rocky Mountains that was deposited to form the rock layers now exposed by the incision of Wild Horse Creek. Water, whether in the form of liquid, ice or vapor, is a significant agent of change affecting the earth’s surface throughout geological time.

As part of this theme of geologic change, the effects of climate and climate change on the landscape are also evident in this painting. Wild Horse Creek is an intermittent stream, flowing seasonally during wetter periods and dry during dry periods, typical of minor streams in semi-arid climates like those of the Great Plains. Erosional processes that affect the creek valley are most pronounced during flash floods, the result of the heavy rains during thunderstorms. To a geologist’s eye, however, the image in the painting evokes wetter times, when significantly larger volumes of water flowed, carving out a broader and deeper valley than would likely be caused by the normal trickle of the stream shown by Sandzén. Much of this erosion probably occurred during the Pleistocene, also know as the Ice Age, during periods of glacial retreat, when the climate was somewhat wetter, and the vegetation was boreal forest, similar to the modern forests of northern Minnesota and Canada. Sea level was lower then, because of the large volume of water held in ice, allowing major rivers like the ancestral Missouri River to cut deeper to base level (or sea level), resulting in the deeper cutting of the tributary stream system into the landscape.

During the Pleistocene, there were intervals when glacial ice extended into Kansas. The surface of parts of northern Kansas is coated by the remains of the sediment left behind by glaciers, and also, for the immediate region shown in the Hillstrom painting, by windblown sediment called “loess,” derived from nearby glacial sediment. These sediments provide the basis for the rich soils whose agricultural promise led early settlers into the Kansas region. Lack of water caused by unusually dry conditions in the 1930s, and poor farming practices, led to the Dust Bowl conditions in this area during the Great Depression. Thus water is a double-edged sword. The rich soils, which were created during wetter periods, must now be irrigated in order to sustain agriculture. This leads to the second geological point regarding Dry Creek Bed, Kansas.

The Ogallala Formation

The exposed rock formations lining the valley walls of the creek bed, indicated with the pinks and creams of Sandzén’s palette, are suggestive of the Ogallala Formation, a fluvial sedimentary deposit derived from ancestral streams flowing off the emerging Rocky Mountains during the period from about ten to two million years ago (the late Miocene to Pliocene periods). The state geologic map verifies that the Ogallala Formation is indeed present in the headward areas of Wild Horse Creek in Graham County. The Ogallala Formation is an extensive unit underlying much of the High Plains, ranging from South Dakota into Texas and eastern New Mexico, covering over 111.4 million acres (174,000 square miles). While relatively thin in the area depicted in the painting by Sandzén, the Ogallala Formation in some locations reaches thicknesses of over 1000 feet. It consists mostly of sands, silts, and gravels, much of it relatively unconsolidated, allowing for good porosity and permeability and making it able to hold large amounts of groundwater. Also called the High Plains Aquifer, the Ogallala Formation is the principal source of water supplying the Great Plains region, with water from it irrigating one-fifth of all U.S. cropland.

Water levels in an aquifer are controlled by the relative differences between “discharge,” the amount of water lost to the aquifer from pumping and from natural processes such as seepage into surface waters and from evaporation and transpiration (from vegetation), and “recharge,” the resupply of the water, principally from precipitation. Because of its semi-arid climate, the region receives relatively low amounts of annual precipitation, with much of that lost to evaporation enhanced by typically steady winds. Coupled with the relative impermeability of the surface over much of the area, which is covered by a hardpan of calcium carbonate called “caliche,” the actual recharge is quite limited. Because discharge from the aquifer greatly exceeds the recharge, water levels have dropped significantly in some portions of the aquifer. Once thought to have virtually unlimited water, the Ogallala Aquifer can now be considered a poster child for critical depletion of groundwater resources.

Before development in the region, recharge and natural discharge were approximately in balance. Use of the High Plains Aquifer for irrigation purposes began in the 1930s, concurrent with rural electrification. Advances in technology for large-scale water extraction were developed after World War II, transforming the region into one of the most agriculturally productive areas in the world. But by 2005, water levels in some areas of the Ogallala Aquifer, including parts of Kansas, Oklahoma and Texas, had declined by as much as 150 feet, according to the U.S. Geological Survey. In these areas, it is estimated that there may be less than a 25-year supply of water remaining. Since development, average water levels in the aquifer have declined about 9%.

Water quality is also an issue. While generally suitable for irrigation purposes, much of the water in the High Plains Aquifer does not meet U.S. Environmental Protection Agency standards. Though much of the contamination is natural, deriving from high concentrations of sulfate, chloride, and other contaminants present in the source rocks, human-generated contamination from sources such as feedlots, and pesticide and herbicide use, is also of concern. Many rural populations in the High Plains depend on groundwater for drinking water, so this is a potentially serious problem.

Although these crucial considerations of the water resources in the area around Wild Horse Creek would no doubt have been deeply interesting and disturbing to Sandzén, it is unlikely that in 1912, when he painted Dry Creek Bed, Kansas, anybody was concerned about the availability or quality of water in the region. It was only near the end of Sandzén’s career and life that factors leading to today’s severe depletion of water came into play, and the Hillstrom painting can serve as a reminder of the pristine, unspoiled quality that was once found there, and, it is hoped, of the need for conservation and preservation, to prevent the world’s natural resources—water being perhaps chief among them—from being spoiled.

James Welsh, Associate Professor and Chair, Department of Geology
Donald Myers, Director, Hillstrom Museum of Art, and Instructor, Department of Art and Art History

Suggestions for Further Reading

Greenough, Margaret Sandzén, unpublished manuscript about Birger Sandzén held in the archives of the Birger Sandzén Memorial Gallery, Lindsborg, Kansas.

Guru, Manjula V., and James E. Horne, The Ogallala Aquifer, Poteau, Oklahoma, 2000.

Lindquist, Emory, Birger Sandzén: An Illustrated Biography, Lawrence, Kansas, 1993.

McGuire, V. L., “Changes in Water Levels and Storage in the High Plains Aquifer, Predevelopment to 2005,” United States Geological Survey, May, 2007 (

Sandzén, Birger, “The Southwest as a Sketching Ground,” The Fine Arts, volume XXXIII, August, 1915, pp. 333-351.

Sandzén, Birger, “The Technique of Painting,” The Fine Arts, volume XXXII, January, 1915, pp. 22-27.

Weeks, J. B., E. D. Gutentag, F. J. Heimes, and R. R. Luckey, “Summary of the High Plains Regional Aquifer System Analysis in Parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming,” United States Geological Survey Professional Paper 1400-A, 1988.