The first of three Pacific Mail Steamship Company paddle wheel steamships, the SS California (1848), contracted for on the Pacific route, left New York City on 6 October 1848. This was before the gold strikes in California were confirmed and she left with only a partial passenger load in her 60 saloon (about $300 fare) and 150 steerage (about $150 fare) passenger compartments. Only a few were going all the way to California. As word of the gold strikes spread, the SS California picked up more passengers in Valparaiso Chile and Panama City Panama and showed up in San Francisco on 28 February 1849. She was loaded with about 400 gold seeking passengers; twice the number of passengers it had been designed for. In San Francisco all her passengers and crew except the captain and one man deserted the ship and it would take the Captain two more months to gather a much better paid return crew to return to Panama city an establish the route they had been contracted for. Many more paddle steamers were soon running from the east coast cities to the Chagres River in Panama and the San Juan River in Nicaragua. By the mid 1850s there were over ten Pacific and ten Atlantic/Caribbean paddle wheel steamboats shuttling high valued freight like passengers, gold and mail between California and both the Pacific and Caribbean ports. The trip to the east coast could be executed after about 1850 in as short as 40 days if all ship connections could be met with a minimum of waiting.

Steamboats plied the Bay Area and the Sacramento and San Joaquin Rivers that flowed nearer the goldfields, moving passengers and supplies from San Francisco to Sacramento, Marysville and Stockton, California—the three main cities supplying the gold fields. The city of Stockton, on the lower San Joaquin, quickly grew from a sleepy backwater to a thriving trading center, the stopping-off point for miners headed to the gold fields in the foothills of the Sierra. Rough ways such as the Millerton Road which later became the Stockton–Los Angeles Road quickly extended the length of the valley and were served by mule teams and covered wagons. Riverboat navigation quickly became an important transportation link on the San Joaquin River, and during the "June Rise", as boat operators called the San Joaquin's annual high water levels during snow melt, on a wet year large craft could make it as far upstream as Fresno. During the peak years of the gold rush, the river in the Stockton area was reportedly crowded with hundreds of abandoned oceangoing craft, whose crew had deserted for the gold fields. The multitude of idle ships was such a blockade that at several occasions they were burned just to clear a way for riverboat traffic. Initially, with few roads, pack trains and wagons brought supplies to the miners. Soon a system of wagon roads, bridges, ferries and toll roads were set up many of them maintained by tolls collected from the users. Large freight wagons pulled by up to 10 mules replaced pack trains, and toll roads built and kept passable by the tolls made it easier to get to the mining camps, enabling express companies to deliver firewood, lumber, food, equipment, clothes, mail, packages, etc. to the miners. Later when communities developed in Nevada some steamboats were even used to haul cargo up the Colorado River as high as where Lake Mead in Nevada is today.