An amendment to the california state constitution can be implemented by

It can be implemented in three ways. One is that two-thirds of the membership of each chamber of the California State Legislature must ratify a proposed amendment, which then becomes a statewide ballot initiative to be approved by a majority of the state’s voters. Another is that the California State Legislature, with approval of 2/3 of both houses, may submit a ballot initiative calling for a Constitutional State Convention, which if approved, would then vote on amendments via chosen delegates from throughout the state. The third is that the electorate may amend the constitution by a ballot proposition. All three ways are based on the constitution of California.

Both were elected by popular vote

Explanation:

The Senate of the United States shall be composed of two Senators from each State, elected by the people. source (google)