In the early 1830s, a few fur trappers from the Pacific Northwest exploring southwards into the San Joaquin Valley arrived just in time to be greeted with a sight of horror. An epidemic of smallpox and malaria brought unintentionally by the Europeans had swept down the San Joaquin River corridor during the summer of 1833, killing in a single stroke between 50 and 75 percent of the entire native population in the valley. The outbreak did not vanish; it continued year after year with diminishing acuteness until about 50,000–60,000 indigenous people lay dead. Explorer Kit Carson noted in 1839 that "... cholera or some other fearful scourge broke out among them and raged with such fearful fatality that they were unable either to bury or burn their dead, and the air was filled with the stench of their decaying bodies."