The Walla Walla AVA was established in 1984 with its boundaries amended in 2001. Mostly contained within Washington, a portion of this appellation does extend south into Oregon. Of the region's , nearly were planted as of 2008. Along with its wine, Walla Walla is known for its sweet onions, which is a local food and wine pairing favorite, especially the Merlot grown within the appellation. The region is generally wetter than the rest of the Columbia Valley, receiving more than 20 inches (50 centimeter) of rain on average each year. The area between the town of Walla Walla east to the Blue Mountains is the wettest with each mile from the city eastward to the mountains seeing an addition inch of average rainfall. The Walla Walla AVA contains at least four distinct soil profiles scattered across the valley - slackwater terrace, loess, river gravel and flood plain silt. The majority of Walla Walla's vineyards are located on a combination of slackwater terrace and loess. The silt and volcanic ash that make up the region's loess soils contain remnants from the eruption of Mount Mazama (which also formed the Crater Lake nearly away in Oregon).