The earliest separately issued map of Trinity Bay, which appeared in Duflot de Mofras' report of his travels on the West Coast of North America.

In 1839, Eugene Duflot de Mofras, was assigned to the embassy in Mexico City and instructed to visit the northwestern provinces of Mexico, report on potential commerce, observe U. S., British, and Russian interests, and determine feasibility of French posts in the region. De Mofras visited Jalisco, Colima, Sinaloa, and Sonora in 1840, then sailed from Mazatlán to Monterey. He met with commandant Mariano Guadalupe Vallejo in Sonoma, continued to Fort Ross, and returned to Monterey in July. On September 1 he sailed up the Sacramento River with A.G. Rotchev, manager of Fort Ross, to New Helvetia, where he met with John Sutter, with whom Rotchev was to initiate negotiations for sale of the Russian fort. He later visited San Jose, Santa Cruz, and San Francisco, before travelling to the Hudson Bay Company's Fort Vancouver. On this trip, de Mofras met and talked with Charles Wilkes. He returned to San Francisco with Hudson Bay Company director Sir George Simpson and factor John McLoughlin and U.S. agent Horatio Hale to Monterey. On January 3 1842, de Mofras sailed via Santa Bárbara to San Diego, before returning to Mexico.

Duflot de Mofras provided important information on its economic life, foreign involvement, and geography. He provides excellent descriptions of the Russian posts at Ross and Bodega just prior to their sale to the United States, notes Sutter's willingness to serve France, and reports on the reputed plot of Isaac Graham to overthrow Mexican government in California.