Pools typically are small, covering at most a few score square meters. Shallow soils prevent forests from developing. Pools form in the small depressions following winter rains. Lasthenia glaberrima, Limnanthes douglasii rosea, Navarretia tagetina. Most species are active in winter, flower in spring, and spend summers as seeds waiting for the return of fall rain.
Pools range in size from a few score square meters to several hectares.
Shallow soils over bedrock prevent woodlands from establishing. The pools fill at the onset of fall rains and dry by evaporation during warm spring weather. Plagiobothrys undulatus, Psilocarphus brevissimus. Surrounding high ground, however, usually is mantled with chamisal rather than grassland. Fe-Si cemented hardpan prevents downward drainage of rainwater.