What is "tri-valley"

Tri-Valley is a triangle-shaped region in the eastern San Francisco Bay Area. The area is 18 miles southeast of Oakland and 33 miles from San Francisco. It encompasses the cities of Pleasanton, Livermore, Dublin, San Ramon, and Danville which includes Alamo, Blackhawk, Camino Tassajara, Diablo, Norris Canyon, and Sunol in the three valleys from which it takes its name: Amador Valley, Livermore Valley and San Ramon Valley. The region is well known for its Mediterranean climate, wine region, historic downtown areas, high cost of living and fine dining. It is a primarily affluent suburban area with a population of about 360,000.