Geology of Devil's Den State Park

Journal of the Arkansas Academy of Science Volume 7 Article 20 1955 Geology of Devil's Den State Park James E. Case University of Arkansas, Fayetteville Francis B. Connelly University of Arkansas, Fayetteville Follow this and additional works at: http://scholarworks.uark.edu/jaas Part of the Geology Commons Recommended Citation Case, James E. and Connelly, Francis B. (1955) "Geology of Devil's Den State Park," Journal of the Arkansas Academy of Science: Vol. 7 , Article 20. Available at: http://scholarworks.uark.edu/jaas/vol7/iss1/20 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact , . • Journal of the Arkansas Academy of Science, Vol. 7 [1955], Art. 20 GEOLOGY OF DEVILS DEN STATE PARK JAMES E. CASE and FRANCIS B. CONNELLY University of Arkansas INTRODUCTION Arkansas Devils Den State Park is located in southern Washington County, (in parts of secar the northwestern boundary of the Boston Mountain Province West). 25, 26, 35, and 36, Township 13 North, Range 31 The park is ions 23, 24, Arkansas Highway 170, about 18 miles southwest of West Fork and 15 miles northwest of Winslow. Both of these towns are on U. S. Highway 71. For a better understanding of the sequence of geologic events in the park 22 and 27 in the western part of the to study sections area, it was necessary park. Similarly, since sections 35 and 36 added little information of geologic interest, they were deleted from this investigation. As a result, the discussed area includes sections 22, 23, 24, 25, 26, and 27, and these sections wil1 be referred to as the park area. The region was mapped during the late winter and early spring of 1953 by plane table surveying, from air photographs, and by compass traverse. PHYSIOGRAPHY The area has a relief of more than 800 feet, and the mountains have elevations in excess of 1,800 feet. These mountains are erosional remnants in the Boston Mountain Plateau, which has been dissected deeply in this area by two streams--Lee Creek to the east and Ellis Branch to the west (Figure 1). The stream pattern is generally dendritic, but Lee Creek is conspicuously abraided in sections 24 and 25 where it courses through the Bloyd shale. The streams cut through the Brentwood and Pitkin limestones in other parts of the park area. The streams join in the north central part of section 34 at an elevation of about 980 feet above mean sea level. The region represents late youth in the erosion cycle. This is evidenced by the flat-topped mountains which are the remnants of the original plateau and also by the stage of development of the drainage system. ' ¦ STRATIGRAPHY The surface rocks are Upper Mississippian and Lower Pennsylvanian in age; they are well exposed at many points, especially along the streams. However, in places, there has been an extensive amount of slumping of the Atoka sandstone on the underlying Atoka and Bloyd shales, and several critical points of investigation have been covered. Mississippian System. The Mississippian system in the Devils Den area is represented by the Pitkin formation which is in the Chester series (all age determinations are from Croneis, 1930). The formation crops out along Lee Creek from below the dam in section 26 southwestward into section 35 (Figure 1) and forms the surface rock over much of the east central part of section 26. Along Ellis Branch it is well exposed in the creek bed and in its valley in the south central part of section 27. Pitkin Limestone Format ion. The Pitkin formation is a light-colored, gray °r blue-gray limestone which is often dense and is sometimes massive. The normal thickness of exposed limestone is a little more than 30 feet. The formation is composed of several limestone beds of different textures which range from finegrained, sublithographic in lower parts to medium and coarse grained near the upper portions. Most of the beds show a rough crinoidal weathering in outcrops where the formation is a scarp former. There is local development of oolitic limestone in the lower and middle portions of the formation. Near the top of the ¦itkin formation is a well-defined zone of nodular, crossbedded, fine-grained calcareous siltstone. At a place about 300 yards downstream from the dam in section 26, there is an exposure of blue and tan shale below the limestone. This e xposure is about eight feet thick and contains small lenses of sublithographic limestone and a few concretions. It is lithologically different from the brown or black Fayetteville shale which ordinarily underlies the Pitkin formation non- < I! I 67 I Published by Arkansas Academy of Science, 1955 67 ' Journal of the Arkansas Academy of Science, Vol. 7 [1955], Art. 20 ARKANSAS ACADEMY OF SCIENCE 68 are also from Croneis, the Pitkin formation. conformably (contact relations has been referred to 1930); therefore, the shale On weathered surfaces the Pitkin formation is usually a very light gray color. Lichens and mosses often grow on the exposed face of the rock. Where streams have cut across the formation the rock has a smooth surface and a pale blue color. Numerous potholes have been developed by stream abrasion and solution. The weathering of the nodular zone in the upper part of the formation can be observed in the lichen-covered, crumbly ledges in the southeastern part of section • 27. One cave has been developed in the Pitkin by the solution of the limestone by ground water. The cave, Farmers Cave, is 25 yards northwest of the county road bridge over Ellis Branch in the south part of Section 27. The formation is generally fossiliferous, but collecting is difficult because of the hardness of the rock at most exposures. The bryozoan, Archimedes, is fairly abundant. There are many assemblages of gregarious horn corals. Brachiopods, coiled cephalopods, and bryozoans can be seen in section or relief in many of the stream exposures. The Pitkin formation is overlain unconformably by the Hale formation. Hale Format ion. The Hale formation is the oldest of the Pennsylvanian rocks in Northwest Arkansas. It is the basal formation of the Morrow group, which is Pottsville in age. The formation outcrops along the valley walls of Lee Creek and Ellis Branch in sections 26 and 27 The average thickness of the formation is about 140 feet. A large shale interval comprises the lower part of the formation in the park area, and true thicknesses are difficult to measure because long, gentle, covered slopes have developed (...truncated)