Question: Within Four Corners of the United States, which unit of the National Park Service has ruins of the indigenous tribes and is within the boundaries of the Navajo Nation?

The Four Corners is a region of the United States consisting of the southwestern corner of Colorado, southeastern corner of Utah, northeastern corner of Arizona, and northwestern corner of New Mexico.  The Four Corners area is named after the quadripoint at the intersection of approximately 37° north latitude with 109° 03' west longitude, where the boundaries of the four states meet, and are marked by the Four Corners Monument.  In addition to the monument, commonly visited areas within Four Corners include Monument Valley, Mesa Verde National Park, Chaco Canyon, and Canyon de Chelly National Monument.  It is the only location in the United States where four states meet.  Most of the Four Corners region belongs to semi-autonomous Native American nations, the largest of which is the Navajo Nation, followed by Hopi, Ute, and Zuni tribal reserves and nations.  The Four Corners region is part of a larger region known as the Colorado Plateau and is mostly rural, rugged, and arid.  The most populous city in the Four Corners region is Farmington, New Mexico, followed by Durango, Colorado. <SEP>  Located in northeastern Arizona, it is within the boundaries of the Navajo Nation and lies in the Four Corners region.  Reflecting one of the longest continuously inhabited landscapes of North America, it preserves ruins of the indigenous tribes that lived in the area, from the Ancestral Puebloans (formerly known as Anasazi) to the Navajo.  The monument covers 83840 acre and encompasses the floors and rims of the three major canyons: de Chelly, del Muerto, and Monument. Canyon de Chelly National Monument ( ) was established on April 1, 1931 as a unit of the National Park Service.  These canyons were cut by streams with headwaters in the Chuska mountains just to the east of the monument.  None of the land is federally owned.  Canyon de Chelly is one of the most visited national monuments in the United States. <SEP> The Navajo Rangers (formed 1957) are an organization of the Navajo Nation in the Southwestern United States, which maintain and protect the tribal nation's public works and natural resources.  The Rangers form a part of the Navajo Nation Department of Resource Enforcement (within the Division of Natural Resources), and currently consists of 16 officers in four different field locations.  The Rangers also serve as a park service, protecting natural and historical sites and assisting travelers. <SEP> The Grand Canyon Escalade is a proposed entertainment complex on the eastern rim of the Grand Canyon within the boundaries of the Navajo Nation.  Located to the north of the confluence of the Colorado River and the Little Colorado River, the project has been touted by Scottsdale based developers as a way to bring money to the tribe.  However, this has not been without controversy, as there has been significant opposition from those who want to preserve the area.  Strong opposition has also come from members of the Navajo Nation who live in the surrounding region and have cited numerous ecological, economic, and spiritual concerns with the proposal, as well as ethical concerns with the background of the developers.  The Hopi have also expressed complete opposition to the project, citing the sacredness of the area surrounding Little Colorado River confluence.  As of 2017, development of the project has been stalled and appears to be in a state of uncertainty, as the proposal has been rejected by three of the four key governing committees of the Navajo Nation, and continues to face opposition from Navajo Nation President Russell Begaye and other tribal leaders.