The Santa Monica Mountains, adjacent to the Pacific Ocean just west of Los Angeles, California, have low elevation, high relief and a Mediterranean climate. To date 122 species of bryophytes have been found, especially in the moist drainages. Species that were common (about half of the 122) were compared in terms of microhabitat variables (substrate softness, moisture, slope and shadiness) and in how they distinguished mesosites (varying vascular vegetation types, elevation, parent rock type, distance to the coast and insolation). This constitutes a descriptive comparison of the ecologies of the species in the flora. Acrocarpous mosses, pleurocarpous mosses and liverworts tended as groups to differ in some habitat preferences. Only a few bryophyte species were strong indicators of vascular vegetation type. The diversity of sampled mesosites was to a great extent explicable as a scaling-up of the variety of microsites that each contained, thereby allowing for a diversity of bryophytes in a biome that might generally be characterized as inhospitable.