After the Mexican Cession, and California was annexed by the U.S. in 1848 and became a state in 1850, Robinson worked for the Pacific Mail Steamship Company, and as a land manager during the 1850s through the 1880s.
In 1868 he formed the Robinson Trust with Abel Stearns, the most important land owner in Southern California in Los Angeles County.
The real estate sales partnership included four San Francisco investors; Samuel Brannan, E. F. Northam, Charles B. Polhemus, Edward Martin.
In order to gain maximum coverage for their campaign, they linked themselves to the 'California Immigrant Union' and helped guide that organization’s sales pitches.
In 1846, Alfred Robinson published Life in California, a comparatively sympathetic portrait of the lifeways and Californios political vicissitudes of the region under the Mexican Republic.