 As the 1830s drew to a close , the fur industry slowly began to die as silk replaced beaver fur as a desirable clothing item . By this time , also , the beaver population of streams in the Rocky Mountains had been decimated by intense hunting . Furthermore , frequent Native American attacks on trading posts made it dangerous for employees of the fur companies . In some regions , the industry continued well into the 1840s , but in others such as the Platte River valley , declines of the beaver population contributed to an earlier demise . The fur trade finally disappeared in the Great Plains around 1850 , with the primary center of industry shifting to the Mississippi Valley and central Canada . Despite the demise of the once @-@ prosperous trade , however , its legacy led to the opening of the American West and a flood of settlers , farmers , ranchers , adventurers , <unk> , financially bereft , and entrepreneurs took their place . 
