How did the western frontier of the us come to a close

The western frontier of the US refers to the westernmost states of the United State. As a result of the American victory in the American revolutionary war, American gained formal control of the western states where the British control before. These lands were mostly given as rewards to veterans of war and the locations are regarded as frontiers because, they contained less than two people per square mile.
During the period of 1849 to 1892 a lot of development arise which made people to flock to these areas, especially during the industrial revolution.
By 1893, the frontier were declared closed because they are now well populated with people.