Los Coronados consist of four rugged islands that lie 15 miles south of Point Loma, San Diego, and 8 miles west of the Mexican mainland opposite Tijuana. South Island, the largest, is 2 miles long and 0.4 miles wide, with a maximum elevation of 672 feet. North Island, approximately 2 miles distant, is 1 mile long, 0.12 miles wide, and 467 feet high. Middle Island and Middle Rock are much smaller and lie close to the northern tip of South Island. All of the islands have steep slopes (often precipitous on the western, or windward, sides) and are sparsely vegetated (Figure 1). There are no permanent sources of fresh water. General descriptions of the islands, and their vegetation may be found in Osburn (1909) and Nelson (1921). The history of the islands has been reviewed by Ellsberg (1970).