On the bark of Arizona cypress (Cupressus arizonica) in shady creek.
There were several of these mats among the selaginella. about an inch across and flat. Firm to the touch. Under shade on the edge of a wash. I could go back for a better picture if needed.
Liverwort at base of a north facing cliff on Barry M. Goldwater range. Plant turns black when dry
Liverwort. But none of the suggestions look correct.
Growing in the water being dropped by an air conditioner.