[2] In early 1849 as a sailor he heard of the discovery of gold and left New York drawn by the California gold rush and came to San Francisco in June 1849, working as a dock worker unloading ships, while regularly prospecting for precious ores in the local mines.

There in the estuary, he assembled this more powerful 70 hp steamboat and began successfully shipping cargo and carrying passengers on the Colorado River from its mouth, up to Fort Yuma.

Johnson was instrumental in getting Congressional funding for a military expedition to explore the Colorado River above Fort Yuma in 1856.

Johnson had delegated operations to his senior steamboat captain Issac Polhamus, and distracted by his rancho and political career, did not invest in more shipping to keep up with the growing traffic caused by the 1862 Colorado River gold rush.

By 1864 it had created a large backlog of undelivered freight and caused competition of opposition lines to arrive on the Colorado River.

This finally forced Johnson to expand his fleet of steamboats and to begin to use barges to increase their cargo-carrying capacity.