Lava caps are late seral communities of annual herbs, perennial shrubs, and a few depauperate (a kind of semi bonsai) tree species. They are open rocky areas on ridgetops or ridge ends within the forest, and especially on Peavine Ridge. These ridges are formed by pre-historic volcanic mud flows, (Mehrten Formation) and centuries of erosion, and the result is a field of rocks. Among these lichen covered rocks and manzanita skeletons are wonderful displays of annual and perennial wildflowers. These wildflowers include the yellow bur Navarretia (Navarretia prolifera ssp. lutea), and the Pleasant Valley Mariposa tulip. (Calochortus clavatus var. avius).
Lava caps have suffered many impacts as they were viewed as non-productive sites for trees so have been used as low value areas by loggers. Old skid trails, old roads, and old tractor-built piles are in evidence.
Now there is a more dangerous thing happening to lava caps. They are becoming degraded by not only by logging, but invasive weeds which include several annual grasses and of late, two kinds of star thistle. Many of these weeds came with early grazing. Climate change associated with drought may already be having effects too.
We should enjoy these unique areas while we can, because some of them are disappearing.