Typical outcrop of 1.4 billion year old granite in Alderfer/Three Sisters Park.

This article was initially published in 2014. Between then and now, the link to the full document was lost. Thankfully, we’ve just been able to recover a copy of the document, thanks to generous efforts by the USGS. We’ve embedded the document in our own library, for safekeeping. This repost will lead you to the full story of the geologic history of Jeffco’s Open Space Parks, as they were in 2014.

Jefferson County straddles one of the most conspicuous and important geographic and geologic boundaries in western North America, the eastern flank of the Rocky Mountains. To the east you can travel 1,100 miles across Great Plains and Central Lowlands before you sight the western foothills of the Appalachians. If you travel in the other direction you will cross or skirt mountain range after mountain range until you sight the Coast Range near San Francisco, more than 900 miles to the west. Many of these mountains have different ages and origins than the Colorado mountains, but they are all part of the great mountain belt called the North American Cordillera that extends along the western edge of the continent from Alaska through Mexico. Read more