Information on storm petrels of the Pacific Coast of North America includes reports by early egg and specimen collectors of pelagic observations, beach-wrecked specimens, cursory visits to nesting islands, and taxonomic discussions. Aside from accounts of nest sites and nesting islands, little basic biological information is available. Osborne and Reynolds (1971) surveyed nesting populations of sea birds along the California coast and Osborne (1972) intensively studied nesting rocks from the Oregon border to Cape Mendocino, Humboldt County, California. The present study was conducted to document the status, chronology, and ecology of nesting storm petrels in northern California. STUDY AREA Most work was on Little River Rock, 2 miles S of Trinidad, Humboldt County, California, 41"02' N, 124"09' w, with occasional visits to other nesting islands in northwestern California. With the nossible exception of Castle Island, Del Norte Count;, Little River Rock supports the largest population of nesting Leach' s Storm Petrels (Oceanodroma leucorhoa) and Fork-tailed Storm Petrels (0. fur&u) in California. Little River Rock is a basalt sea stack, about onequarter mile offshore, with a surface area at sea level of about 2 acres. Mostly bare rock, it has two nearly vertical peaks interconnected by a saddle of ancient marine deposits of sand and shells. The east peak is a conical dome about 75 ft in diameter and 75 ft high. The west oeak is 126 ft high. has a flat triangular top about-50 ft wide, and-the west side drops precipitously 40 ft to a rock and soil-covered slope about 30 x 75 ft in size. Intensive studies were confined to accessible areas of the west peak. The rock has four general vegetation types. Coastal brushfields of Bacchuris pilulnris 2 ft high cover about half the west peak and a mixture of Bacchuris, Guultheriu shallon, Gurryu elliptica, and Rhus diuersilobu to 4 ft high covers most of the east peak. The shrubs have an understory of grasses. The soil is 6-8 inches deep with a loose texture, allowing easy excavation by burrowing petrels. Portions of the east peak and half the top and the entire scree slope of the west peak are vegetated predominantly by stands of Festucu culifornicu, Elymus mollis, Fruguriu chiloensis, and Scrophuluriu culifomicu. These areas have a thick sod and rocky soils to 9 inches deep. Steep rocky slopes with poor soil and moisture retention support growths dominated by DudZeyu furinosu, Sedum sputhulifolium, Mesembryunthemum chilense, and Pluntugo Zunceolutu. The soil in these areas ranges from a few plant fragments to mixtures of organic and rock particles 3 inches deep. Some sheltered pockets hold clumps of Elymus mollis and