Alcatraz Island later invalidated the sale and paid Frémont nothing. Frémont and his heirs sued for compensation during protracted but unsuccessful legal battles that extended into the 1890s. Following the acquisition of California by the United States as a result of the Treaty of Guadalupe Hidalgo (1848) which ended the Mexican–American War, and the onset of the California Gold Rush the following year, the U.S. Army began studying the suitability of Alcatraz Island for the positioning of coastal batteries to protect the approaches to San Francisco Bay. In 1853, under the direction of Zealous B. Tower, the United States Army Corps of
Escape from Alcatraz (triathlon) foot race, but by making it an out-and-back run rather than a one-way course, became known as a "Double Dipsea". The course has remained the same over the years and celebrated its 35th anniversary in 2015. Participants are limited to members of the Dolphin Club and The South End Club. The Dolphin Club is the host and sponsor of the event. The annual public Escape from Alcatraz triathlon, organized by IMG, now takes place in early June. The current course consists of a swim starting near Alcatraz Island, a run from the bay to the transition zone at Marina Green,