Carey was educated in Aghabullogue, learning land surveying. In April 1849, at age 15, he left Ireland without his family, a few months before the onset of the Great Famine. He travelled first to England before arriving in Boston in July. He went to the Pacific Coast where for 18 months he worked surveying the California-Arizona border. As a contractor, he conducted field work for Robert C. Matthewson, deputy surveyor for the U.S. federal government, and worked in Mexico and Baja California. After the onset of the 1849 Gold Rush, he went north to San Francisco to pan for gold in the mountains. He met some success but continued to work as a surveyor up and down the West Coast. He arrived at Fort Victoria on 11 May 1859, just over a decade after leaving Ireland.