Geology

Geology 512x219

The Wichita Mountains are a spectacular natural setting for a wildlife refuge. 


Two rugged ranges of granite mountains trend nearly east-west and enclose a natural prairie. These granite walls and the canyons that cut through them offered protection to groups of Native Americans hiding from their enemies. In the 1800's, when the U.S. Cavalry thought about where to build forts to keep the peace in the Indian Territory, it was only natural to build Fort Sill on the margins of the Wichita Mountains. At the beginning of the 20th Century, when conservationists thought about where it would be best to bring in herds of buffalo and other endangered species, the protected prairie sheltered by the Wichita Mountains was a logical choice.

The rugged yet protected landscape of the Wichita Mountains Wildlife Refuge is the result of over half a billion years of geologic history. The first known geologic event in this region took place 550 to 600 million years ago (Early of Middle Cambrian time). The land from northern Texas to north of the present Wichita Mountains sank, forming a basin which filled with sea water. Rivers carried clay, sand and gravel into this sea and thick layers of sediments were formed. These rocks have been penetrated by deep wells both north and south of the Wichitas, but within the mountains, the only remnants are small outcrops of Meers quartzite. Small masses of this altered sandstone are exposed along Medicine Creek north of Mt. Sheridan and along the road a little north of the refuge's Meers entrance. The quartzite is compact, dense and varies from white to gray.
Sometime after the deposition of the sediments, a hot lava formed at considerable depth below the surface in the Wichita area. The liquid was forced up into the overlying sediments and spread out between the sedimentary beds. In the Meers area, the lava tore off large fragments of the roof sandstone and altered it to dense compact quartzite.

The lava cooled slowly, forming a dark gray to black igneous rock known as gabbro. There are several large outcrops of this rock in the Wichita Refuge. One outcrop straddles the northern boundary, extending 12 miles northwest from west of Lake Lawtonka to North Mountain. Another outcrop, approximately one square mile in area, is present in Cutthroat Gap where it also forms the lower part of the valley walls. A large outcrop of this dark rock occurs north and west of Quanah Parker Lake and extends three miles west to north of the Fish Lakes. An extension of the band may be seen around headquarters and Kiowa Lake.

After the solidification of the gabbro lava, the area was uplifted thousands of feet. This uplift was accompanied by erosion and the overlying sediments were removed, with the exception of the small remnants of Meers quartzite. The erosion continued exposing the gabbro at the surface and even stripped away part of this rock.
The next major geologic event took place in the Middle Cambrian time (500 to 550 million years ago). A hot granitic lava developed at considerable depth below the surface and was forced upwards into the overlying gabbro and also in part reached the surface through volcanic vents. The cooling of this hot liquid at depth formed a red granite which is the most extensive rock in the refuge. Mt. Scott is composed of this granite. Trees grow only on the gabbro and the contact between the two rocks can be detected by the tree line. This contact can be traced northwest for several miles and dips to the south. The granite intruded the gabbro as a sheet a few hundred feet thick. 

The granite exposed in the southern part of the refuge from Quanah Mountain westward to Charon's Garden is more coarsely crystalline than that forming Mt. Scott. The age of a very coarse granite dike in Charon's Garden was determined at the Carnegie Institution of Washington as 500 to 550 million years old.

The hot lava which reached the surface poured out and congealed to a rock resembling granite but much finer grained, known as rhyolite. It is red in color and in places has small crystals embedded in a very fine grained ground mass. In addition to the rhyolite lava, considerable material was hurled out of explosive volcanoes and settled from the air into layers of volcanic breccia. 
Lava flows and associated explosive volcanic material comprise the major part of the rocks exposed in Fort Sill Military Reservation to the refuge's south. In the Wichita Refuge, lava flows are present in a belt south of Mt. Scott, extending from Elmer Thomas Lake westward along Little Medicine Creek for a couple of miles and in places northward across the paved highway.

After the formation of the lava, the land sank, producing a basin which filled with sea water. The earliest sediments deposited in this sea are Upper Cambrian in age, probably a little less than 500 million years old. This sea persisted for many million years, and the sediments formed during this time are present in the "Slick Hills" a few miles north of Meers. The sediments are sandstone overlain by limestone. These rocks were removed by erosion from the refuge area.  

The mountains of the Wichita region were formed some 300 million years ago (Pennsylvanian period). They were created by a tremendous uplift accompanied by large folds and faults. Some of the faults were miles in length and produced large blocks. Some of these settled with respect to others, and the large flat areas bordering the Scenic Highway in the central part of the refuge probably originated by faulting.

The mountains originally were considerably higher than the present ones as erosion has stripped off the upper parts and deposited this material in the intervening flats, reducing the relief. Most of this erosion took place in Permian time (some 250 million years ago) and produced extensive gravel deposits. Remnants of these gravels may be seen north of Crater Lake, north of Lake Elmer Thomas, east and south of Lost Lake, and in several other parts of the Refuge. Granite is the dominant rock of the refuge, and the gravels formed by erosion are mainly composed of granite fragments. There are unconsolidated well-rounded boulders 6 to 18 inches in diameter, known as cobblestones, surrounded by yellow-to-brown clay. Below the weathered surface they are well cemented.  

The main geologic event that has taken place since is the erosion of most of the Permian gravels which once covered this area. In recent times, some newer gravels have been deposited along the small streams and in the flats. These can be seen around Lake Lawtonka, along Sandy Creek, Wolf Creek, and in other areas of the refuge. Boulder slides in the drainage depressions are common on many of the steep slopes. One of the best examples of boulder accumulation is the "River of Boulders" on the south side of Mt. Scott. 

This information is an excerpt from the C.A. Merrit, School of Geology, University of Oklahoma and the Programs in Geosciences at the University of Texas at Dallas.