Overview

The Larkspure area is characterized by a rich geological landscape that includes a variety of rock formations and structures. The western portion features Precambrian metamorphic and igneous rocks, while the eastern region comprises Mesozoic sedimentary layers, including sandstone, shale, and limestone. A prominent feature in the area is the Perry Park Fault. This fault creates striking geological formations, including cliffs and valleys. The varied geology of Douglas County gives rise to grasslands, forests, and unique wildlife habitats.

The Geology of Sandstone Ranch

The Sandstone Ranch spans billions of years of geologic time. It is a great location to view the Great Unconformity. The Great Unconformity is a huge gap in Earth’s geologic record, where much younger rocks sit directly on much older rocks. It is like opening a book and finding that hundreds of millions to over a billion years of pages were torn out. Unlike ordinary unconformities, the Great Unconformity shows up across large parts of the earth, not just in one local area. The broad extent suggests a large-scale event or series of events that stripped away rock or stopped new layers from forming over a huge region.

The “Great Unconformity,” a nonconformity where the Cambrian Sawatch Sandstone lies directly upon the Precambrian granite basement, is spectacularly exposed in the northwestern quarter of the quadrangle along Gove Creek on the Sandstone Ranch. Faulting is generally responsible for the juxtaposition of rocks of Paleozoic through Tertiary age adjacent to Proterozoic rocks along the mountain front.  Thorsen, 2008.

Tava Sandstone is also visible, and is perhaps the only physical evidence of the period known as “snowball earth” known at this time.

The document below was developed by volunteers for Douglas County.