Where to Find Agate in Wyoming

Wyoming carries a small but distinctive agate roster. Sweetwater agate, from the Sweetwater River drainage in Fremont and Sublette counties, is a saturated red-and-white banded chalcedony with a translucent core, eroded out of Pleistocene gravels along old shorelines. Youngite, named for the Young Ranch near Hartville in Platte County, is a brecciated pink chalcedony with a druzy quartz coating. Petrified-wood agate turns up across the Eden Valley and Blue Forest beds in Sweetwater County, often replaced by clear-to-blue chalcedony. Smaller showings of moss and dendritic agate occur on the Powder River breaks in eastern Wyoming, mostly as small float on ranch country. The most productive ground is in Sweetwater River gravels (Fremont County), Hartville uplift, Youngite (Platte County), Eden Valley and Blue Forest petrified wood (Sweetwater County).

Casual hand collection of common rocks and minerals like agate is allowed on most BLM and U.S. Forest Service land in Wyoming, with daily and annual limits set by the local field office. National parks, most state parks, and tribal land are off-limits. Always confirm rules before a trip.

Sweetwater River gravels (Fremont County) is the standout. Other strong ground includes Hartville uplift, Youngite (Platte County), Eden Valley and Blue Forest petrified wood (Sweetwater County).