Amache National Historic Site Act This bill directs the National Park Service (NPS) to establish, when sufficient land within the exterior boundary of what is to be the Amache National Historic Site has been acquired to constitute a manageable unit, to establish such historic site in Colorado as a unit of the National Park System to preserve, protect, and interpret for the benefit of present and future generations resources associated with the incarceration of civilians of Japanese ancestry during World War II at Amache, also known as the Granada Relocation Center, and the military service of incarcerees at the Granada Relocation Center. The NPS may acquire by donation or purchase any land or interests in land located within the exterior boundary of the National Historic Site, except that the NPS may acquire personal property associated with the purposes of the historic site only by donation. The NPS must prepare a general management plan for the historic site. The NPS may enter into agreements with public or private entities to establish and operate facilities outside of the exterior boundary of the historic site for administration, visitor services, and curation of personal property; and other public or private entities to carry out this bill.