The Ochoco Reservoir country east of Prineville is laced with small agate and jasper beds along the creeks, and Congleton Hollow is the one people name: limb casts, red and yellow jasper and enough loose material along the cuts to fill a bucket in an afternoon. Ochoco National Forest and BLM, largely free collecting, but the mapping is a patchwork so run the ownership layer before you dig a hole.
Jasper, agate, limb casts
See it on the map
Other places on the map within a couple of hours.