You have to do 70 missions to unlock las venturas and where it says no fly zone thats area 69 it sometimes has a ufo flying above it but I never saw but if you want to go there just spawn a hunter then activate vehicle of death cheats and wait for the ufo. I went their when I completed high stakes low rider but I not allowed there until you do the mission verdant meadows which is probably the last mission you have to do to get to las venturas I think so good luck :)
