California has 53 U.S. House districts. This year, in nine of them, no Republican filed to be on the June 5 primary ballot.
In 2016, in November, there were nine U.S. House districts in California with no Republican on the ballot. For November 2018, it is not now possible to know how many districts will have no Republican on the ballot. On the one hand, there might be Republicans who file as write-ins in the June primary. Because there is only one person on the primary ballot in the 13th, 19th, and 32nd districts, it is possible a Republican write-in will place second in any of those districts and thus appear on the November ballot.
On the other hand, even in races in which a Republican is on the primary ballot, there are probably a few districts in which no Republican in those districts will place first or second. There are always U.S. House districts in California with two Democrats who place first and second, even though a Republican is running.
Concerening the qualified minor parties in U.S. House races, there are nine Greens, five Libertarians, two members of the American Independent Party, and one member of the Peace & Freedom Party. Independents are running in 19 of the 53 districts.