After Alta California was ceded by Mexico to the United States in 1848 with the Treaty of Guadalupe Hidalgo, the islands' environment became linked to the growth of the city of San Francisco. Beginning in 1853, a lighthouse was constructed on SEFI. As the city grew, the seabird colonies came under severe threat as eggs were collected in the millions for San Francisco markets. The trade, which in its heyday could yield 500,000 eggs a month, was the source of conflict between the egg-collecting companies and the lighthouse keepers. This conflict turned violent in a confrontation between rival companies in 1863. The clash between two rival companies, known as the Egg War, left two men dead and marked the end of private companies on the islands, although the lighthouse keepers continued egging.