On side of sage scrub trail, in mixed cryptogamic mat along with mosses, Crassula connata, and Riccia trichocarpa. I often see Riccia spp. and Asterella palmeri around here but this is the first time I have seen Sphaerocarpos in a (relatively) non-anthropogenic habitat. This thallus was unaccompanied by visible conspecifics.

Across the road (but not directly across) from this tree:
https://www.inaturalist.org/observations/147445061

At roadside. Oddly enough, many other seemingly suitable Sphaerocarpos habitats at the H did not have any visible specimens.