In 1864 Congress passed the Homestead Act, which allowed (mostly white) people to claim land in the west, including Colorado. They could come get land almost for free as long as they could farm it and make it profitable in 5 years. This was called "proving up". Very few people did it successfully because much of the land was dry and difficult to farm.
Eventually ammendments to this law opened it to noncitizens coming across the ocean, to single women, to native americans if they left their communities, and to black people who had formerly been enslaved. These formerly enslaved folks were called "Exodusters".