I would not recommend a red maple (Acer rubrum) for San Diego, because it's not suited to your climate. Although red maple is native to a broad range of climates from Canada to Florida, it does best in Zones 3-9 in more humid climates. Many wonderful trees will do well in your climate, however. One favorite is drought-resistant, ever-green live oak (Quercus agrifolia). This tree can be slow growing at the start, but once it's established it needs minimal watering during the summer. The tree often attracts California sister butterflies, as well as a variety of birds. Live oak usually grows about 50 feet tall and wide. It's hardy in Zones 9-11, meaning it's perfectly adapted to your area's mild winters. For smaller trees you might consider California buckeye (Aesculus californica), Jerusalem thorn (Parkinsonia aculeata), or western redbud (Cercis occidentalis).