By editor
Fallon, Prairie County
Sixty million years ago, silica-rich fluids filled voids in volcanic rock with chalcedony. Trace amounts of iron and manganese oxide seeped in, branching out in dendritic patterns that look exactly like fossilized moss. The host rock eroded, and the Yellowstone River carried these stones eastward. Today, the gravel bars around the town of Fallon are the epicenter for finding Montana moss agate.
Visitor Access
The gravel bars are accessible from public fishing access sites and bridge crossings. Collecting is free, but anyone twelve or older must hold a Montana Conservation License (eight dollars for residents, ten dollars for non-residents) to legally access state trust lands and fishing access sites along the river. The best hunting is in the late summer and fall, after the spring floodwaters have receded and exposed fresh gravel.