The dark-colored rock at the bottom of the canyons is Precambrian in age, dated at 1.7 billion years old. These rocks were originally sedimentary rocks, but were changed into metamorphic rocks and partly melted into igneous rocks when the area that is now Colorado collided with ancient North America and became part of the continent. There is a huge gap in the geologic record at the contact of these rocks with the overlying red sedimentary rocks. The record of about 1.5 billion years of earth's history is missing! We know from surrounding areas that this region was uplifted into a major mountain range which, after hundreds of millions of years, was finally eroded low enough that sediments could be deposited where the mountains once stood.
Precambrian Black Canyon Group
Last updated: February 24, 2015