His voyages supplying the Army at Fort Yuma demonstrated that the river was navigable by steamboats.
Negligence caused it to sink at its dock below Fort Yuma, and was then washed away before it could be raised, in the spring flood of May 1853.
Turnbull who meanwhile had returned to the Delta from San Francisco with another cargo and a more powerful engine for the Uncle Sam.
Turnbull later turned up in Mazatlan, Mexico, where he ran a small steamboat for many years and attempted to promote the building of a canal.
However Turnbull had shown the worth of steamboats to solve Fort Yuma's supply problem and to successfully navigate the Colorado River, an example that was soon followed by George Alonzo Johnson.