American interest in the area after Alaska's acquisition by the United States in 1867 was limited until gold was found in the Yukon Territory in the 1880s. George Holt was the first American known to have explored the lower Copper River, in 1882. In 1884 John Bremner prospected the lower river. The same year a U.S. Army party led by Lieutenant William Abercrombie attempted to explore the lower river, and found a passage to the country's interior over a glacier at the Valdez Arm. In 1885 Lieutenant Henry Tureman Allen fully explored the Copper and Chitina rivers, going on to cross the Alaska Range and enter the Yukon River system and eventually reaching the Bering Sea. The Allen expedition also noted the use of copper by native peoples along the Copper River. Several other expeditions explored the coastal regions in the late 1880s, and some attempted to climb the mountains. An 1891 expedition led by Yukon explorer Frederick Schwatka descended the Nizina, Chitina and Copper Rivers from the north.