Have been finding these on and off in the same area for the last several years. Always growing on the side of the trail and in mixed woods but it appears to be live oak or madrone that are the closest. They grow close to the ground and the cap coloration varies, usually some shade of brown but some of these had stronger vinaceous tones than what I've seen before. The spore size fit within the values that Thiers gives in "California Mushrooms" The largest specimen was only 7.0 cm across the cap.