San Marcos is a city in the North County region of San Diego County, California. As of the 2020 census, the city's population was 94,833. 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.

Discovery Lake is a small man-made reservoir located in San Marcos, California offering a wildlife refuge.

Double Peak is located south of San Marcos, California. The elevation at the summit is 1646ft, and approximately 1,000 feet (305 m) above the north foot of the mountain.

Rancho La Costa Reserve is a small area but packed with excellent trails and a great mix of easy to moderate to advanced. The best trails are found on the south slope of the mountain and can easily be ridden as a series of up-down loops.