A great resource for finding the ancient time period of bedrock of a locale. The link below provides high resolution versions of the map including full CMYK printing files if needed.

U.S. Geological Survey
Geologic Investigations Series I-2781

The North America Tapestry of Time and Terrain
By: Kate E. Barton, David G. Howell, José F. Vigil

https://pubs.usgs.gov/imap/i2781/