Around 1842, George Simpson, Matthew Kinkead, Robert Fisher, Jim Beckwourth, and other traders helped build El Pueblo, a multiethnic settlement on the north bank of the Arkansas River at the international boundary between Mexico and the United States. Built in the style of a Mexican placita and constructed primarily of adobe bricks, it served as a trading post where Native Americans, Americans, Europeans, and Mexicans exchanged guns, powder, beads, whiskey, agricultural products, and livestock until 1848, when most inhabitants left for the California Gold Rush. Accounts describe a plaza used for trading and housing animals, a blacksmith shop, and many low-doored rooms used as homes, all enclosed by four adobe walls with two round guard towers and designed more to prevent theft than withstand attack. On December 24, 1854, after tensions between Native Americans and newcomers had escalated, a group of Ute and Jicarilla Apache Indians killed or captured all occupants inside El Pueblo as residents were already moving to New Town at the mouth of the Huerfano River about thirty miles south. The site was later used as a corral and domiciles, many of its adobe bricks were reused in early Pueblo buildings, and El Pueblo eventually disappeared beneath the city.