The Mexican Frontier, 1821–1846 published by other historians. This work was supplemented by additional primary materials which he discovered in the archives that allowed him to delve further into certain areas. "The Mexican Frontier" examines the southwestern United States, specifically the areas now known as Arizona, California, New Mexico, and Texas, in the twenty-five years between Mexico's independence from Spain and the beginning of the Mexican–American War. This resulted in the transfer of control of the border areas to the United States. In the early days of the Republic of Mexico, these areas comprised its northern border, including the territories of Alta California and
Rancho Santiago de Santa Ana County given under Spanish Rule which were rare during this time. This was only two and a half months before the start of the war for Mexican Independence (1810-1821). The surrounding land grants or ranchos were granted by the Mexican government after Mexican independence in 1821. José Antonio Yorba built an elaborate adobe hacienda, El Refugio (the Refuge), located near present-day First and Sullivan Streets in western Santa Ana. With the Mexican Cession of California to the United States following the Mexican-American War, the 1848 Treaty of Guadalupe Hidalgo provided that the land grants would be honored. As required by