This past April I went out to Anza Borrego State Park, just east of San Diego, and saw several Cacti in bloom! The goal of the trip was to view the super bloom of wildflowers. Cactus blooms had not crossed my mind and felt like a pleasant surprise.
On the South side of the park near Highway 78, there is a campground called Tamarisk Grove Campground. Across the street from the campground, is a small hiking loop with Cacti on display. We actually missed that loop and journeyed off on a trail where we could eventually see it, but we dis see lots of Cacti and some wildflowers too!