Riviera is a recruitment firm, not an investment firm, so I'd assume their data comes from positions they've been hired to fill.

Yeah, I thought the scope was far too limited to be of any use outside of a small (but admittedly significant) area.

While the data is from the Bay Area I find it's correct for my situation working in SoCal for a startup. It is at least a decent gauge to see if you are way below or above the salary ranges. Unfortunately, it won't help someone in a rural area.