We have various waterfalls in the San Diego backcountry which you can visit including: Green Valley Falls, Cedar Creek Falls, Three Sisters Falls and Merrigan Trail Falls. They run strong on occasion if we've had some good winter rain.
A fairly difficult hike, Three Sisters Falls is by far the most popular. Please be prepared and do some research if you're attempting this hike.
Green Valley Falls and Merrigan trail falls are much easier hikes for families and smaller children. Carry plenty of water and plan your hike early to avoid the scorching afternoon sun. Please be careful on the trail and watch out for rattlesnakes.