Fun find! I will have to watch when my internet is being nice.
You might also look up Craters of the Moon Idaho. Geography-ish things can be interesting.
That's just south of Challis.
Where I grew up in Oregon we found petrified logs in some of our pastures. Nothing big, but some were a couple feet long and 12-16" diameter. Some friends of ours had an opelized wood mine too.
Locally petrified wood is rare but it is found occasionally. An uncle has several baseball sized pieces. Shark teeth are common, lots of fossils in shale rock too.
Years ago I drove through the little town of Calistoga, right next to Napa CA. They have a petrified redwood log, 6ft in diameter. It was impressive. Got pictures somewhere in box... this pic is from the net though...