Over near Oceanside there is a independent facility that verifies manufactures estimates. This covers everything from engine output, to performance numbers & handling characteristics (If you read Car & Driver often, you'll notice quite a few of their car test or first drives are based in southern California or Ocenside).

Also, both Ford & GM do some final testing on upcomming vehicles in real world stop & go conditions. Unfortunately, the cars they test here are usually within months of Job-1, so by the time you take a picture & send it in, the car mags already have a "preview" article on it.

I've caught a group of current gen Cavaliers crusing around downtown early one morning, about 6 months before production, a facelifted Contour, and the SN95 Mustang on display for certain dealers & stockholders, but by the time the pics I sent in would have appeared in mags, they had their own stories & pictures. News embargoes don't help either.

All 3 automakers have proving grounds about 4-5 hours away in Arizona, and also pretty much everone does testing up in Death Valley from late July to late August. There is no shortage of disguised cars there, you just have to figure what it is you're looking at. Most anything you see there is likely to be about a year or more away from production.

Couple of weeks ago I came across what looked like a larger right hand drive version of a Q45 at the pub across & down the street from the Star of India w/ mounted instraments, so I'd say there is no one area, though downtown during off peak hours, or weekends is probally the best single area.

 

Thanks guionM!