San Diego County borders the Pacific Ocean in the extreme southwestern corner of the United States. The coast line extending from the Mexican border northward for 70 mi. is a continuous series of sandy beaches and high bluffs broken by rivers, bays, and lagoons. Because of ideal living and working conditions, development of the costal area has been rapid, until more than 500,000 people reside there today. The area will undoubtedly continue to grow and a population of over 3,000,000 by the end of the century is predicted.