Final answer:
California's top-two primary system can result in a general election with both candidates from the same party and is open to all candidates regardless of party affiliation, but it's a recent development and does not bar third-party candidates from running (3).
Step-by-step explanation:
Features of California's top-two primary system include the possibility of having a general election where both candidates are from the same political party, which occurs because all candidates run against each other regardless of party affiliation. This system is a type of primary election used in California state-level offices, U.S. Senate, and House elections, and is not restricted by party lines.
However, the top-two primary system has not been in place since the ratification of the state constitution but is a more modern development. Third-party candidates are not legally prohibited from running in the general election; they can run if they manage to be among the top two candidates during the primary. Thus, the features of the top-two primary system include its nonpartisan nature and the possibility that it can result in general election matchups without third-party candidates if they do not receive enough votes in the primary.