Pleistocene (Illinoian) lake deposits are exposed in the Doby Springs area, Harper County, Oklahoma. The collapse basin in which these beds were deposited resulted from solution of salt or anhydrite in the underlying Permian strata. The rim of the basin is made up of the Permian Whitehorse group, the Pliocene Ogallala formation, and the Pleistocene (Kansan to Yarmouth) Crooked Creek formation.

In Kansan time a southeastward-flowing stream cut through the Ogallala formation into the Permian strata. This stream deposited the gravels, sands, and silts of the Crooked Creek formation in its valley. During Yarmouth time a caliche formed in the top of the formation. In Illinoian time a collapse basin formed in the Doby Springs area. Lake sediments containing the Doby Springs local fauna were deposited in this basin. Settling and collapse along the southern edge imparted the present dip to the lake beds. In Sangamon time the area was drained, and a caliche formed in the upper part of the lake sediments; later, further collapse occurred to the north and imparted the northward dip to the northern part of the initial basin deposits. The present outward radial drainage results from the collapse on the margins of the initial basin. The alluvial deposits along the modern streams are of Wisconsin and Recent age.

The Doby Springs local fauna contained in the Illinoian lake deposits consists of the remains of ostracods, mollusks, fishes, amphibians, reptiles, birds, and mammals. The seven fishes (white sucker, creek chub, flathead chub, fathead minnow, black bullhead, green sunfish, and yellow perch) indicate a cool, upstream, lake environment with smaller streams running into the lake.

Twenty-four forms of mammals from the Doby Springs local fauna are discussed, and a new species of the mammalian genus, Peromyscus, is described.

The following extant small mammals indicate a marsh environment with surrounding lowland meadows and some trees: arctic shrew, masked shrew, northern water shrew, shorttail shrew, muskrat, meadow vole, and jumping mouse.

The climate in the area is determined by plotting the present-day distribution of the living forms and arriving at an area of overlap. This area of overlap for the species recorded in the Doby Springs local fauna lies in southeastern North Dakota and northeastern South Dakota. The climate in Oklahoma during Illinoian time was probably similar to that in the area of overlap today. Lower summer temperatures and more effective moisture are indicated.

The Doby Springs local fauna is correlated with the Berends local fauna, Beaver County, Oklahoma, and the Butler Spring local fauna, Meade County, Kansas.

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