San Marcos is a city in the North County region of San Diego County in the U.S. state of California. As of the 2010 census, the city’s population was 83,781. It is the site of California State University San Marcos. The city is bordered by Escondido to the east, Encinitas to the southwest, Carlsbad to the west, and Vista to the northwest. Lake San Marcos is an enclave, or county island, in the southwestern part of the city, within San Marcos’ sphere of influence but technically an unincorporated community.
According to the United States Census Bureau, the city has a total area of 24.4 square miles (63 km2). 24.4 square miles (63 km2) of it is land and 0.02 square miles (0.052 km2) of it (0.08%) is water. Due to the moderating influence of the nearby Pacific, temperatures rarely fall below freezing in winter and above 100 degrees F. in summer. Like most of coastal San Diego County, cool overcast from the Pacific is common in May and June (“May gray”, “June gloom”). July through September are usually the warmest months, although hot and dry Santa Ana winds can strike any month (most commonly August) and raise risks of wildfires. Most of the rain falls between November and March, averaging about 13 inches per year, with up to 20 inches falling in the San Marcos Hills.