This is a typical flat to find loose chalcedony. There are areas of Basalt and Rhyolite that you will find the sources of all of the agate and chalcedony. Once you understand lava flows from the Oligocene volcanics... you are on your way to finding the most unusual chalcedony in the world.
Step into a Forest Service Office, get the large scale Forest map(s) you need, inquire as to where a good area to begin looking might be... and you are on your way. Make sure you mark where you camped... so you can find it next time and finish looking over the beautiful hillsides.