When did the first two female senators from the same state concurrently serve in the U.S. Senate?

In 1993, for the first time, two female senators from the state of California concurrently served in the U.S. Senate, Dianne Feinstein and Barbara Boxer. Both of them were Democrats. The two of them were elected in 1992. Feinstein assumed office the same year after the special election, with Boxer assuming office in 1993.

After a failed gubernatorial campaign in 1990, Feinstein won a 1992 special election to the U.S. Senate. Feinstein was elected on the same ballot as her peer Barbara Boxer, and the two became California's first female U.S. Senators.

Feinstein and Boxer have served in tandem for more than 20 years, but it is, actually, not a record for the pairs of senators. J. Thurmond and Ernest Hollings from South Carolina, for example, have been working side by side for 37 years!