Question: McElmo Phase refers to a period in the late 11th and early 12th centuries, when drastic changes in ceramics and masonry techniques in Chaco Canyon appeared, archeologists initially suggested that the McElmo influence was brought to Chaco Canyon by immigrants from which site located in Montezuma County, Colorado, it protects some of the best preserved Ancestral Puebloan archaeological sites in the United States?

Context articles: Chacra Mesa
McElmo Phase
Mesa Verde National Park
Kin Kletso
Peñasco Blanco
Lowry Pueblo
Pueblo Alto
Dune Dam
Hungo Pavi
East Community

The Chacra Mesa is a high mesa massif composing the southwestern flank of Chaco Canyon, a region that is notable for its rich collection of Ancestral Puebloan archaeological sites.
McElmo Phase refers to a period in the late 11th and early 12th centuries, when drastic changes in ceramics and masonry techniques in Chaco Canyon appeared.
 During this period the Ancestral Puebloans living in the canyon started using painted black-on-white pottery versus their standard grey ware, and the masonry and layout of great houses built during the McElmo phase, which was the last major construction era in the canyon, differ significantly from those built during the early parts of the Bonito Phase (850 to 1140), which overlaps with the McElmo Phase.
 Archeologists initially suggested that the McElmo influence was brought to Chaco Canyon by immigrants from Mesa Verde, but subsequent research suggests that the developments were of local origin.
 Archeologist R. Gwinn Vivian notes, "The jury is still out on this question, a problem that poses intriguing possibilities for future work."
Mesa Verde National Park is a National Park and World Heritage Site located in Montezuma County, Colorado.
 It protects some of the best preserved Ancestral Puebloan archaeological sites in the United States.
Kin Kletso is a Chacoan Ancestral Pueblo great house and notable archaeological site located in Chaco Culture National Historical Park, 25 miles southwest of Nageezi, New Mexico, US.
 It was a medium-sized great house located 0.5 miles (0.8 m) west of Pueblo Bonito; it shows strong evidence of construction and occupation by Pueblo peoples who migrated to Chaco from the northern San Juan Basin in the time period of 1125 to 1200 (McElmo Phase of Chacoan Architecture).
 From its masonry work, rectangular shape and design Kletso is identified as Pueblo III architecture by prominent Chaco archaeologists Stephen H. Lekson and Tom Windes.
 They also argue that this great house was only occupied by one or two households.
 Fagen writes that Kletso contained around 55 rooms, four ground-floor kivas, and a two-story cylindrical tower that may have functioned as a kiva or religious center.
 Evidence of an obsidian production industry were discovered here.
 The house was erected between 1125 and 1130.
Peñasco Blanco ("White Bluff" in Spanish) is a Chacoan Ancestral Puebloan great house and notable archaeological site located in Chaco Canyon, a canyon in San Juan County, New Mexico, United States.
 The pueblo consists of an arc-shaped room block, part of an oval enclosing a plaza and great kiva, along with two great kivas outside the great house.
 The pueblo was built atop the canyon's southern rim to the northwest of the great houses in the main section of the canyon.
 The building was constructed in five distinct stages between AD 900 and 1125.
 A cliff painting (the "Supernova Pictograph") nearby may record the sighting of a supernova on July 5, 1054 AD.
The Lowry Pueblo is an Ancestral Puebloan archaeological site located in Canyons of the Ancients National Monument near Pleasant View, Colorado, United States.
 The pueblo was constructed around 1060 AD atop abandoned pithouses from an earlier period of occupation.
 It was occupied by 40 to 100 people at a time for 165 years.
 The structure was built up to about 40 rooms and featured multiple kivas.
 The architecture of Lowry Pueblo was influenced by the settlement at Chaco Canyon, approximately 100 miles to the south.
Pueblo Alto ("High Village" in Spanish) is an Ancestral Puebloan great house and archaeological site located in Chaco Culture National Historical Park, northwestern New Mexico, United States.
 The complex, comprising 89 rooms in a single-story layout, is located on a mesa top near the middle of Chaco Canyon; 0.6 miles (1 km) from Pueblo Bonito, it was begun between AD 1020 and 1050.
 Its location made the community visible to most of the inhabitants of the San Juan Basin; indeed, it was only 2.3 miles (3.7 km) north of Tsin Kletsin, on the opposite side of the canyon.
 The community was the center of a bead- and turquoise-processing industry that influenced the development of all villages in the canyon; chert tool production was also common.
 It shares its mesa with another great house, Nuevo Alto, both of which are now protected within the borders of Chaco Culture National Historical Park.
 Storerooms at Pueblo Alto opened to the outside rather than into the interior rooms and there was a huge midden of pottery.
 This and chert found in the midden came mostly from the Chuska area 70 km (43 mi) to the west.
Dune Dam is a long sand dune that lies at the western end of Chaco Canyon, New Mexico, near the confluence of the Chaco and Escavada Washs.
 The dune was created by winds that brought sand up the Chaco River.
 When the dune was large enough, it dammed the Chaco Wash and created a small and shallow lake near the Ancestral Puebloan great house, Penasco Blanco.
 Archeological evidence suggests that the dune was breached around 900 CE.
 Chacoans filled the breach with masonry sometime in the early 11th century, and built an accompanying reservoir lined with stones that was visible until 1920.
 The dam stopped Chaco Wash from further deepening, which helped raise the water table in the canyon, aiding Chacoan farming.
 The absence of a lacustrine plain behind the dam led geologist Stephen A. Hall to question this interpretation.
Hungo Pavi is an Ancestral Puebloan great house and archaeological site located in Chaco Canyon, northwestern New Mexico, United States.
 A set of ruins located just 1 mile (2 km) from the ruins of Una Vida, Hungo Pavi measured 872 feet in circumference.
 Initial explorations revealed 72 ground-level rooms, with structures reaching four stories in height.
 One large circular kiva has been identified.
 Its ruins now lie within Chaco Culture National Historical Park.
East Community is an Ancestral Puebloan great house community and archeological site located 12 miles east of Pueblo Bonito, at the eastern end of Chaco Culture National Historical Park, New Mexico.
 Archeological evidence uncovered during the 1980s suggests the site was occupied by both Chacoans and Mesa Verdeans.
 Eighty-two structures have been identified in the area, including a great house that contains twenty-five rooms and several small house sites.
 At least one kiva has been uncovered there, but no great kivas.
 A partial road segment is visible there, but archeologists are unsure of it connects with a longer segment thought to originate near Pueblo Pintado.
 The great house at East Community was constructed in the 10th century, with significant additions completed during the 11th century.
 The associated small house sites were occupied by Chacoans from 875 to 1300, and thirty-nine of them by Mesa Verdeans, from 1175 to 1300.
 Archeologist Thomas Windes believes the site was linked to Chaco Canyon through a system of signaling stations atop the area's mesas.