Giants general manager Bobby Evans said Tuesday that Frandsen joined the River Cats.
The 33-year-old Frandsen is a native of San Jose who last played in the majors for Washington in 2014. He was released by the Nationals at the end of spring training and signed a minor league deal with the Diamondbacks, who released him last weekend. Frandsen was batting .309 with seven RBI and two doubles for Triple-A Reno.
A career .259 hitter in parts of eight big league seasons, Frandsen posted on Facebook a note thanking his friends, family and fans for their support during a "crazy" couple of months. He and wife Amanda soon will welcome a baby.