MDA DataQuick, a real estate information service. To see how sales performed in Southern California, click here: SoCal real estate. Last month's 45% year-over-year sales gain in the Bay Area was the highest for any month since April 2002, when sales shot up 49%. However, last month's jump is partly the result of the exceptionally weak activity in September 2007, a record low for that month in DataQuick's statistics back to 1988. Year-ago sales plunged after a credit crunch that struck in August 2007 made "jumbo" mortgages -- used to buy higher-end homes -- more expensive and harder to obtain. Entry-level sales were already hurting from the subprime mortgage industry meltdown earlier in 2007. Although sales rose in some coastal communities in September, it was the region's less expensive inland markets that pushed sales up so sharply. Contra Costa, Napa, Sonoma and Solano counties combined accounted for nearly 62% of Bay Area sales, compared with 52% a year ago. Solano County sales doubled from last year, while sales nearly doubled in Contra Costa and Napa counties.