A drive up the 79 eventually brings you to Cuyamaca Lake, a little community in the hills to the east of San Diego city. The lake is a popular destination for boating, fishing, and other relaxing activities. It's also a popular day trip for local campers (there's tons of camping around the area).
The dam that creates the lake was built in 1888 and is touted as the second oldest in California. This lake is popular with fishermen, as it's stocked with many different types of fish. It is situated at an elevation of 4600 feet in an Oak and Pine forest and surrounded on 3 sides by the 26,000 acre Cuyamaca Rancho State Park of which 52% is classified as wilderness.
For more information: Lake Cuyamaca Info.