According to this article, it is likely that the only two candidates on the November 2016 ballot in California’s 46th district will be Democrats. In the primary, there are four Republicans running, and three Democrats. It is probable that with four Republicans in the race, no Republican will manage to place first or second. The 46th district is in Orange County, California’s third-most populous county. No incumbent is running, because the incumbent, Loretta Sanchez, is running for U.S. Senate.
California has used top-two in two elections so far, 2012 and 2014. Although there have been some November U.S. House races in those years between two Democrats in Los Angeles County, so far there have been no Democrat-versus-Democrat general election races in any of the U.S. House races to the south and east of Los Angeles County. Those counties include Orange, San Diego, Riverside, and San Bernardino Counties, all very populous.