During the war with Mexico, "Warren" acted as a guardship at Monterey, California and eventually moved to San Francisco, for duty as a stores and receiving ship. On 13 November 1846, the former sloop-of-war's launch, in charge of Acting Master William H. Montgomery, departed the ship with $900.00 to pay bills accrued by the Navy for supplies, bound for Sutter's Fort, up the Sacramento River. By the end of the month, when no word came from the launch's crew, "Warren's" commanding officer felt "great anxiety" and sent out a hired boat with some men from his ship to hunt for the missing craft and its crew. On 18 December, the search party – having combed the river and inlets as far as Fort Sacramento—returned and reported finding no sign of the launch or of the crew.