The Santa Ana River is probably best known as a concrete ditch where it flows through Orange County, or a huge sandy wash in San Bernardino. For the most part, it is dry or almost dry, and probably isnt noticed by most people. The headwaters of this river are around Big Bear Lake and Mt. San Gorgonio in the San Bernadino mountains. Some of the western drainage of Mt. San Jacinto also flows into this river. Although generally not noticed by residents of the city, this is the river Riverside was named after.
Although most people wouldnt recognize this river as anything more than a dry wash, it has had its share of horrendous floods. This river was diverted around Anaheim long ago so its fertile floodplain could be used for orchardland (the orchards are now long gone, replaced by suburbia). In the days of the orchards, a big storm dumped 20 inches of rain in the mountains and the river came ripping back through anaheim and demolished much of the town(if anyone knows when this storm happened, let me know as i've forgotten the exact year, i think it was in the 30s or 40s) After this flood the huge dam was constructed which you see driving down Highway 91 towards Riverside. Along with a few other dams this is supposed to prevent a similar disaster from recurring. Perhaps this is the case, although in these days of concrete-coated hills and bizarre weather, one never knows.