NORTH BAY -- The median price paid for a home in the North Bay continued to rise in September, with prices in the Bay Area climbing to the highest level in more than four years, according to San Diego-based real estate data tracker DataQuick.

The median price paid for a home in Sonoma County was $335,000, up 9.1 percent from the same month in 2011. Marin County prices increased 3.4 percent, to $650,000. The median price paid in Napa County was $345,000, up 9.5 percent from September 2011.

The number of homes sold decreased year-over-year in Sonoma County, down 5.5 percent, to 446. That number rose 12.1 percent in Marin, to 268, and 1.6 percent in Napa, to 126.[poll id="41"]

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In the Bay Area as a whole, the median price rose 17.5 percent compared to September 2011, to $429,000. The number of homes sold rose 1.5 percent, to 6,850.

A shift in the mix of home sales helped drive regional trends, with foreclosure resales at half of their level last year and a decrease in the percentage of homes sold below $500,000, according to DataQuick.

The low point in the current cycle was in March 2009, when the median price for a home sold in the Bay Area was $290,000. At the high point in June and July of 2007, the median price was $665,000.

Jumbo loans -- mortgages above $417,000 -- accounted for 37.1 percent of purchase lending in September, down from 38.8 percent in August and up from 32.1 percent at the same time last year. DataQuick noted that jumbo loans accounted for 17.1 percent of purchase lending in January 2009 and, before the so-called "credit crunch," reached 60 percent in August 2007.

Adjustable rate mortgages accounted for 11.7 percent of purchase loans in the Bay Area, down from 12.8 percent in September 2011. Government-backed FHA home purchase loans for first-time buyers accounted for 15.9 percent of mortgages in September, down from 21.7 last year.

Foreclosure resales in the Bay Area accounted for 13.9 percent of resales, down from 25.4 percent last year. Foreclosure resales peaked in February 2009, at 52 percent. Short sales accounted for 23.5 percent of Bay Area resales, down from 24.4 percent last year.

Absentee buyers, typically investors, purchased 24.1 percent of Bay Area homes in September, up from 21.9 percent last year. 28.4 percent of purchases were all-cash, up from 27.5 percent in September 2011. "Home flipping" has accelerated this year, according to DataQuick, with 3.9 percent of sales in September occurring within six months of a prior sale of the same property.

"It's obvious that a lot of fence-sitters are getting active. We're probably past the most attractive of mathematical sweet spots, the one that combines low interest rates and low prices. In other words, price increases in the past few months outweigh mortgage rate declines," said John Walsh, president of DataQuick, in the report.