Date of this Version
Rocks cropping out along the North Platte River valley at Lake McConaughy provide a glimpse into Nebraska's geologic past. Here are excellent exposures of the Ogallala Group, which consists of continental sedimentary rocks deposited during the Miocene epoch of the Tertiary period of geologic time. This group of rocks extends throughout much of Nebraska (see geologic bedrock map on outside back cover) but is overlain in most places by younger stream and wind deposits of Pliocene(?) and Pleistocene age. Easily accessible, the Ogallala outcrops contain locally abundant fossils of seeds, casts of pedotubules, and occasional fossils of vertebrate animals such as rhinoceroses, horses, elephants, and camels. Pedotubules are tubular openings in soil. They may have been made by plant roots or by worms, insects, or other animals.
The vicinity of Lake McConaughy is significant to the state both geologically and economically because it is underlain by water-saturated gravel and sandstone deposits that yield water for irrigation, livestock use, and human consumption