Was sort of surprised to see so many amphipods allongside sowbugs here in golden gate park - want to get a better pic with a macro lens next time
This is a mystery liverwort that I've seen at Las Trampas too. Small, blue-green, mid-ribs, growing on exposed trail-side soil in chaparral. I don't think the Las Trampas location had serpentine, but I'm not 100% sure.
No reproductive structures, and the thallus-only key seems to get microscopic pretty quick (air chambers?!). Still, this one was weird: kind of aquamarine, growing on very exposed soil in the dryest part of the chaparral, and those weird little Y-shaped channels at the ends of the leaves. Leaves were almost entirely sessile.
If I make some assumptions in the key, this might be R. glauca: whitish-green thallus, central groove narrows and disappears proximally. However, Doyle & Stottler say both like "slow-to-dry habitats," but I've only ever observed this in the shaded margins of chaparral. Wet patches in dry places.
Observed in Las Trampas Regional Wilderness, Contra Costa County, CA, USA. visible area ~3-4 cm.