There is hereby created within the boundaries of Nez Perce County, within the state of Idaho, a preserve to be known as Lewiston preserve, the boundaries of which are described as follows:  all that territory on both sides of the Clearwater River between Spalding and the Eighteenth Street Bridge across the Clearwater River, in the city of Lewiston, Idaho, and the north and south highway on the north side of the said Clearwater River, and Camas Prairie railroad on the south side of said Clearwater River.