Theres a small Mexican restaurant in Costa Mesa CA called El Taco. 
They make a red sauce that they use for red burritos and red
Quesadillas.  The sauce has meat in it.  I need to find out how to
make it!

gardervillian...

I'd suggest going straight to the horse's mouth.
Even if we come up with a similar recipe, it's
very unlikely to be the sauce you've come to love.

My Grandpa paid $125 for the recipe for egg-nog
made by a posh restaurant in Washington, D.C.,
and it became a family tradition at Christmas.
I inherited the recipe when he passed away, and
consider it priceless. Just my 2¢...

sublime1-ga

Greetings!  You may want to persue the following links I found with a
simple search of the pgrase "Mexican Red Sauce" on Google Search:

Red Sauce Recipes
http://mexicanfood.about.com/cs/redsauce/

I also agree with sublime-ga that you should go directly to the source
if you want the exact same sauce as the restaurant serves.