Geological Trail Intro Part 1

Introduction 

City of Rocks National Reserve is part of the Basin and Range geologic province. Basin and Range topography results from crustal extension. As the crust is stretched (pulled apart), high angle faults develop. Along these faults, mountains uplift and valleys drop, creating the distinctive mountain ranges and wide valleys of theBasin and Range province.  

As rocky ranges rise, the newly exposed rock is immediately subjected to weathering and erosion. This rock is attacked by water, ice, wind, and other erosive agents, that have produced many of the geologic features visible today.  

The majority of outcrops at City of Rocks, and all of the pinnacles, consist of intrusive igneous rock with a granitic composition. Geologists have mapped the two different types of granitic rock within the Reserve as the Green Creek Complex and the Almo pluton.