Hiram Johnson was elected as a Republican in 1910. Johnson was a backer of Theodore Roosevelt and was Roosevelt's running mate on the Progressive ticket in the 1912 presidential election. Johnson continued this affiliation for his 1914 reelection campaign, but returned to the Republican party for his 1916 Senate campaign (through cross-filing, he was also the Progressive nominee in that election).
Hiram Johnson resigned on March 15, 1917 in order to take up his seat in the United States Senate, which he won in the November 1916 election. He was succeeded by Lieutenant Governor William Stephens.
Source for Popular Vote data: California Secretary of State. Statement of Vote at General Election held on November 3, 1914 in the State of California, California Secretary of State (https://archive.org/details/statementofvo19081922cali/page/n71/mode/2up?view=theater) (accessed 20 Sep 2023)