If your guest list is under 25 people, a food truck may be doable and feasible. Keep in mind it takes a long time for a food truck to serve all guests. I went to an event with 40 people and one food truck (tacos only) and it took over an hour for all guests to be served. By then, those who ate first were restless, bored and left.
It would seem that a food truck serving tacos should have had a bunch premade. Maybe the problem is keeping them fresh before serving them. Someone had experienced good results with a taco truck in Orange County, Calif. At work, we had a vendor outside preparing tacos. That was for up to 100 people that worked there.
I missed noticing you were planning the event in the california. I almost assume that tacos are on the menu around here. Someone had mentioned a taco truck/caterer they liked a lot. Sorry If that is not you goal.
I just was looking at the backyard wedding question. That is where I saw mention of Taco Man used by someone. You can find it in that discussion or the number was given as Taco Man +1 (323) 337-2858. I didn't see whether this is a truck or maybe a pull-up cart arrangement, for example.
Sorry I didn't find this earlier. I thought I had a note for it somewhere. Agghh. Too many notes everywhere.