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?

Context paragraphs:
Navajo Rangers: 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.

1993 Four Corners hantavirus outbreak: The 1993 Four Corners hantavirus outbreak refers to the first ever known human cases of hantavirus in the United States.  It occurred within the Four Corners region of the southwestern part of the country.  This region is the geographic intersection where the corners of Utah, Colorado, New Mexico, and Arizona meet.  The region is home to the Hopi, Ute, Zuni, and Navajo Nation Indian Reservations.

Navajo: The Navajo (British English: Navaho, Navajo: "Diné" or "Naabeehó ") are a Native American people of the Southwestern United States.  After the Cherokee, they are the second-largest federally recognized tribe in the United States, with 300,460 enrolled tribal members as of 2015 .  The Navajo Nation constitutes an independent governmental body that manages the Navajo reservation in the Four Corners area, including over 27,000 square miles of land in Arizona, Utah, and New Mexico.  The Navajo language is spoken throughout the region, with most Navajos speaking English, as well.

Navajo Nation Police: The Navajo Nation Police (formerly known as the Navajo Tribal Police) is the law enforcement agency on the Navajo Nation in the Southwestern United States.  It is under the Navajo Division of Public Safety.  It is headed by a Chief of Police, six Police Captains and eight Police Lieutenants.  It includes: Internal Affairs, Patrol, K-9 Unit, Police diving, Tactical Operations Team, Traffic Unit, Fiscal management, Recruitment, and Training Divisions.  The Navajo Nation Police are responsible for seven districts: Chinle, Crownpoint, Dilkon, Kayenta, Shiprock, Tuba City, and Window Rock.  There are also several substations in each district ranging from one-man substations or up to five officers each.  Currently, there are 210 sworn police officers(134 patrol), 28 criminal investigators and 279 civilians, acting as support staff for the department .  There are approximately 1.9% police officers per 1,000 people and one officer is responsible for patrolling 70 sqmi of reservation land.  The Navajo Nation Police are funded by federal contracts and grants and general Navajo Nation funds.  This police department is one of only two large Native American police Departments with 100 or more sworn officers in the United States (the other is the Oglala Lakota Nation's police department).

Navajo Nation Zoological and Botanical Park: The Navajo Nation Zoological and Botanical Park is located in Window Rock, Arizona, the capital of the Navajo Nation.  It is the only tribally owned zoological park in the United States and is notable among zoological facilities in that it labels its exhibits in a Native American Indian language.  Having been operated by the Navajo Nation Parks & Recreation Department since its inception in the early 1960s, it became part of the Navajo Nation Department of Fish and Wildlife in September 2006.

Flag of the Navajo Nation: The flag of the Navajo Nation is the official flag of the Navajo Nation, a Native American Governed Nation in the Four Corners states of Arizona, New Mexico, and Utah.

Grand Canyon Escalade: 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.

Four Corners Monument: The Four Corners Monument marks the quadripoint in the Southwestern United States where the states of Arizona, Colorado, New Mexico, and Utah meet.  It is the only point in the United States shared by four states, leading to the area being named the Four Corners region.  The monument also marks the boundary between two semi-autonomous Native American governments, the Navajo Nation, which maintains the monument as a tourist attraction, and the Ute Mountain Ute Tribe Reservation.

Canyon de Chelly National Monument: Canyon de Chelly National Monument ( ) was established on April 1, 1931 as a unit of the National Park Service.  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.  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.

Four Corners: 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.  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.  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.  The most populous city in the Four Corners region is Farmington, New Mexico, followed by Durango, Colorado.

Supporting paragraphs: Four Corners Canyon de Chelly National Monument
Answer: Canyon de Chelly National Monument