Borthwick traveled in Canada in 1847, south to New Orleans, and then northwards as far as New York, where he lived for some time, until he was struck with gold fever in May 1850, and quickly moved to California. He crossed the Isthmus of Panama at Chagres on a small sailing ship from Panama City, where he stayed until the spring of 1851, reaching San Francisco in the summer of that year. He traveled in gold rush California from 1851 to 1854, eagerly observing and sketching every ethnic group he met.