Alfonso's is a middle-of-the-road Mexican restaurant that is out of place on La Jolla's upscale Prospect Street. The food is just okay, and the decor (inside and outside) is marginal.
They have outdoor seating among loose wood boards and plastic chairs. Inside, the decor is dated and tacky. It is out of the 1970's.
They have a large menu. Appetizers ($3-10) include quesadillas, flautas, nachos, and largeer combination platters. They have many house specialty platters and combination plates ($8-$20). You can also buy soups, salads, and a la carte tacos and other items.
They have a full bar, with many specialty drinks ($6-$7), premium tequilas, and beer and wine.
We were seated promptly and served chips and salsa. Chips were thicker and crunchier than normal. Margaritas were fine. For dinner, I had beef fajitas with sides of rice, beans and guacamole. The fajitas were okay, but served like a stew (choice of red or green sauce) for some reason. My guest had fish tacos that were served with fried fish filets in each taco, instead of baked chunks of fish.
I did not notice another Mexican restaurant in the area of this one. I think that any decent Mexican restaurant could easily succeed in this area at the expense of Alfonso's.