From what I can find out not many californian ranch owners actually left when the southwest became part of the US.

I'm sure there are records of the major families that owned land, sold land etc left (AND do the geneology of the families that left and find out who their decendants are and where they are living-we don't want to do this halfway and have 100,000. people claiming to be Jose Gomez who left his shack in Los Angeles for mexico without bothering to sell the property (probably because of a dispute over some property or someones unmarried daughter or some situation that would prompt a person to drop everything and leave) . The names and geneology there of.

I think that this is a tactic that is beyond the reconquitstas because it actually requires 'research' (which is somthing that from what I have seen they are not inclined to do very willingly)not just shouting what they have been told.

I imagine the conversation would be along the lines of...

"My people were here first and you stole our land."
"Really? What is your name and what ranch did your family used to own?"
"Que?"
"What 'piece' of property did 'your' family used to own here that you are trying to get back. Was it in Malibu, Los Angeles, San Diego San Juaquin, San Bernardino...., Just what property were we to have stolen and from who."
"California. We owned all of California"
"Oh I had no Idea that I was talking to a decendant of the King Of Spain."
"F--K You . Your are F____ing Racist!"
" So your family was never really 'from' here and we stole nothing from you and you are just lying to see if you can take what was never yours. "
" You're a Racist.!!!"
"And you're a lying Thief. You steal our services, our resources and you have stolen 10 minutes of my time. "

Let's punch holes in their "You stole our land" argument bacause I'm getting really pissed off at them lying in our face and getting away with it.

I think the place to start would be at the City Halls.
I guess I could start a Webpage about the old ranches I was going to suggest it be a wiki page but that would be filled up with fabricated geneologies in about 10 minutes.