Pools typically are small, covering under about 50 square meters. These pools fill and empty many times during the winter, and have extremely thin soils over the solid bedrock that prevents downward rainwater percolation. Scattered along the western Sierra foothills between Shasta and Tulare counties, and in the volcanic tablelands of the Modoc Plateau in Shasta, Lassen, Modoc and Siskiyou counties. 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.