The consent of this state is hereby given to the purchase by the United States of such ground in the city of Denver, or any other city or incorporated town in this state, as its authorities may select, for the accommodation of the United States circuit and district courts, post offices, land offices, mints, or other government offices in said cities or incorporated towns, and also to the purchase by the United States of such other lands within this state as its authorities may from time to time select for the erection of forts, magazines, arsenals, and other needful buildings.