There are more Indians in CA than in any other state; however, as part of the population, the highest concentration of Indians can be found New Jersey and New York.

As to why they are so many, most likely because the majority of Indians are highly educated and the Bay area has a high concentration of tech jobs.

“Over one-quarter of employed Indian-born men worked in information technology. 
Among the 713,000 Indian immigrant male workers age 16 and older employed in the civilian labor force in 2008, 27.0 percent reported working in information technology; 20.2 percent in management, business, and finance; 10.7 percent in other sciences and engineering; and 10.6 percent in sales (see Table 2). ”

Retrieved from : Konstantinos Konstantinides  (Sept 2, 2012)   www.quora.com