He remained in this business until the spring of 1849, when he sold it to travel by oxen with his brothers Jacob and James, to California during the gold rush.

There, they engaged in cattle raising and farming on 16,000 acres (6,500 ha) in San Joaquin County.

[3][1][2][4][5] The Sargent Brothers acquired and developed sizable holdings in San Joaquin, Santa Clara, and Monterey counties.

Roswell and Jacob managed the San Joaquin Valley, as well as additional properties around Stockton and Lodi, California.

[2] Sargent was actively involved in Republican Party politics, serving four terms as a member of the California State Assembly from 1871 to 1882.

[1] At the time of his death, he was considered the wealthiest man in San Joaquin County, owning extensive ranches in the northern part of the state and having thousands of head of cattle.