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
Alcatraz Citadel coves and bay. In 1882, the citadel was enlarged to provide more accommodation for the families of the military officers working on Alcatraz. Between 1873 and 1895, 32 Native Americans were imprisoned at the citadel on Alcatraz, including 19 Hopi men held in captivity there between January and August 1895 after being transferred from Fort Defiance. The island continued to develop in the 1880s and in 1898 the population of Alcatraz increased dramatically from 26 to over 450 due to the Spanish–American War and placed a demand for new buildings. The original barracks evolved into Building 64 in 1905. The