A nonpartisan blanket primary is a primary election in which all candidates for the same elected office, regardless of respective political party, run against each other at once, instead of being segregated by political party. It is also known as a jungle primary, qualifying primary, top-two primary or Louisiana primary.In fact, in the 2016 election two Democrats were on California's November ballot running to replace Senator Boxer who had retired. Both had received more primary votes than any Republican or other candidate. Today, all offices elected statewide (instead of by district) are held by Democrats, an outcome irreversible in the foreseeable future.
Under this system, the candidates receiving the most and second-most votes become the contestants in the general election—as in a runoff election, in a two-round system. (In some cases, the second round of voting is necessary only if no candidate receives an overall majority on the initial ballot.)
However, there is no separate party nomination process for candidates before the first round, and political parties are not allowed to whittle-down the field using their own internal processes (e.g., party primaries or conventions). Therefore, it is entirely possible that two candidates of the same political party could advance to the general/run-off.
CA is well on its way to politically resemble post-war Japan or Mexico during the period 1920-2000. That is, a place where all important decisions will be settled within the caucus of the ruling party. There factions representing various populations and interest groups will contest outcomes. Generally, such systems become massively corrupt and patronage-driven. Such has been the case in places like 20th century Mexico, today's New York and, to some degree, Japan.
Full disclosure: my interest is that of a native son; thankfully no longer a resident. I view 21st century CA politics becoming depressingly like those of the third-world - typically squalid and dysfunctional.