Upper Republican is a name archaeologists use for a prehistoric cultural group that occupied the upper Republican River area in northeast Colorado, western Nebraska, northern Kansas, and southeast Wyoming from AD 1100–1300. As a phase of a larger cultural tradition, the Central Plains tradition, the Upper Republican phase represents semisedentary and semihorticulturalist peoples that populated the Central Plains late in the prehistoric era. The Itskari culture was originally considered a subphase of Upper Republican, but recent evidence suggests that this group may have developed separately. While the heartland of the Upper Republican and Itskari cultures is located in western Nebraska, evidence of these prehistoric groups’ presence in Colorado is significant—enough so that occupations are sometimes termed High Plains Upper Republican.

Central Plains Tradition

The Central Plains tradition (CPt) is generally defined by the semisedentary, small-village horticulturalists that populated the region in and around Nebraska during the Late Prehistoric period, AD 950–1400. This cultural tradition is defined in contrast to those more-mobile Woodland groups to the west, including the Apishapa, and those more-sedentary groups of the Mississippian cultures to the east. Three variants of the CPt—the Nebraska phase, the Upper Republican phase, and the Smoky Hill phase—were originally defined with distinct cultural, geographical, and temporal characteristics.

Originating sometime around AD 1000, the CPt was likely established by a combination of internal change from local Woodland cultures and external factors, including the migration and influence from Mississippian populations. From 1100–1300 the expansion of the CPt reached from the High Plains to the Missouri River. However, around 1400 CPt populations began to contract with limited evidence of their presence after 1500. Some argue that the people of the CPt later developed into groups now recognized as ancestral to the Pawnee Nation.

Upper Republican Culture

William Strong first identified the Upper Republican phase as culturally distinct from the Nebraska phase during his work at Lost Creek in the 1930s. Further research, including work by Waldo Wedel and Marvin Kivett at Medicine Creek in southwest Nebraska, has contributed significantly to the understanding of Upper Republican culture. From archaeological contexts, it appears that Upper Republican territory extended from the Republican River valley and the Loup River basin in southern and central Nebraska to the river valleys of northern Kansas, southeastern Wyoming, and northeastern Colorado. Based on the changes in ceramic assemblages, three sequential phases of Upper Republican lifeways have been proposed, including Upper Republican I (AD 100–1250), II (1225–1300), and III (1350).

Upper Republican groups practiced a subsistence economy based on hunting and gathering, as well as the horticulture of maize, squash, and beans. Farming allowed these groups to adopt a semisedentary lifestyle and remain in one location for extended periods of time. Evidence of permanent structures support this theory and suggest that these groups lived within small communities. The exact construction of their houses, called earth lodges, is different among the various phases of the CPt. Within Upper Republican sites, the layout of these single-unit earth lodges was typically square to subrectangular with rounded corners. Rarely were these structures subterranean; instead, they tended to undercut only the topsoil or were built upon the ground surface. Storage pits, dug into the earth, are also common within these structures. Sites that contain evidence of these housing structures have only been identified in Nebraska, including at Medicine Creek, Mowry Bluff, and Dooley. As of yet there is no evidence of these housing structures in Colorado, which may suggest that the High Plains Upper Republican occupations were organized differently than occupations within southwestern Nebraska.

Upper Republican ceramic vessels are typically bulbous and conical-shaped with a cord-roughened exterior and flared rims. Often these rims are decorated with a variety of incised designs, including a preference toward incised parallel horizontal lines. Projectile points tend to be side-notched. Niobrara Jasper (also known as Smoky Hill Jasper) and other flint-like rocks called cherts tend to be the main stone materials used in Upper Republican tool kits. However, there is evidence of extralocal stone materials—including Flattop Chert from Logan County, Colorado—in many Upper Republican sites.

Albeit from a small sample size, it appears that Upper Republican burials consisted of secondary internments of disarticulated remains in large circular pits, often with grave goods. There is evidence that some burials were less ornate, however, where primary individual burials had few grave goods.

Itskari Culture

Originally identified from the Sweetwater site of central Nebraska, Itskari was first classified by Richard Krause as the Loup River phase and only later renamed by John Ludwickson. It is argued that the Itskari culture is a distinct prehistoric group that developed separately, from AD 1000 to 1400, from the Upper Republican complex. The center of Itskari territory is within the lower Loup River basin of central Nebraska, with evidence of their presence expanding into the river valleys of northeastern Colorado and southeastern Wyoming. Three variants of Itskari archaeology have been identified, including Itskari A, B, and C. These three Itskari forms likely represent contemporaneous regional variations over a period of 400 years, rather than sequential phases.

The Itskari practiced a diverse subsistence strategy, including hunting and gathering, fishing, and the use of horticulture. Following a similar social structure, the Itskari likely lived within small communities of single-unit houses. Itskari housing structures tended to be square to oval and constructed around a central basin-shaped fireplace typically made of wattle and daub with built-in storage pits. These structures tended to be smaller than those of Upper Republican populations.

Ceramic vessels of the Itskari tended to be bulbous and conical-shaped, often with handles. Typically these pots were sand-tempered with a cord-roughened exterior and unthickened, collared rims. These rim designs varied by region. For example, it appears that Itskari A sites tend to produce rims with incised and/or studded designs, whereas Itskari B and C rims were more diverse, typically incised with opposed parallel-diagonal lines or v-shaped motifs. Other Itskari ceramics include pipes, with human or animal subjects decorated on the bowl ends. Unlike other groups from the CPt, it appears that the stone tool assemblages of Itskari cultures are dominated by non-local materials, especially materials from the High Plains region.

Burial practices of the Itskari included the use of communal ossuaries, or burial containers, with modest grave goods.

High Plains Sites in Colorado

Several sites within northeastern Colorado have been identified as having Upper Republican and/or Itskari occupations. These groups occupied Colorado river valleys during the initial expansion of the CPt, around AD 1100. For example, the Donovan site in Logan County dates to AD 1100–1300 and was extensively occupied by Upper Republican groups who used this site to process game animals, particularly bison. The Battle Canyon site cluster, including Peavy Rock Shelter in Logan County, Split Rock Cave, and McEndaffer Rock Shelter (both in Weld County), hold evidence of Itskari A and likely Upper Republican I occupations.

At the height of CPt expansion, circa AD 1300, the High Plains were experiencing an influx of Upper Republican and Itskari migrants. Evidence of this is seen in the occupation of several sites in Weld and Elbert Counties. The Happy Hollow site, which dates to 1300, has a ceramic assemblage similar to Itskari A assemblages. However, it appears that Buick Campsite, West Stoneham Pasture, and a third unnamed site in Weld County, each of which date to around 1350, more strongly resemble Upper Republican II assemblages.

After 1400 there appears to be a contraction of the CPt populations. This may be due in part to environmental pressure from deteriorating climatic conditions, as it coincides with the Pacific Warming episode. After 1500 there is only limited evidence of occupation by either Upper Republican or Itskari groups on the High Plains.

The Role of Colorado in the CPt

Although these High Plains sites are multipurpose and exhibit extensive occupations, none of them have evidence of housing structures or of the use of horticulture typical of CPt sites within Nebraska. Therefore, Upper Republican and Itskari occupations of Colorado’s High Plains were organized differently than those of central and southern Nebraska. A few hypotheses have been put forth by archaeologists to define the nature of these High Plains sites and their relation with farming villages to the east.

In the Resident Population hypothesis, Laura Scheiber and Charles Reher argue that what may have at first been hunting camps on the High Plains later became established settlements with cultural connections to the eastern farming villages. Over time these groups established their own High Plains identity.

In the Drought-Induced Residential Mobility hypothesis, Donna Roper argues that the occupation of the High Plains sites was due in part to periods of drought affecting the farming villages on the Central Plains. They suggest that these groups moved onto the High Plains irregularly, when drought affected the farming villages of Nebraska, and not seasonally.

The Hunting Camp hypothesis, according to Michael Page, notes that High Plains Itskari sites tend to be established near stone tool material sources. As there are few quality stone sources found within the heartland of Itskari populations, it is likely that these groups traveled to the High Plains to obtain raw stone. While there are closer lithic sources, including the Niobrara jasper sources in southern Nebraska, they are located in the region dominated by Upper Republican groups. Evidence of brutality and warfare between the Upper Republican and the Itskari groups suggests that territories may have been established. Therefore, it may have been less contentious to travel further onto the High Plains for both lithic resources and hunting opportunities.

The nature of these High Plains sites and of their relationship with Upper Republican and/or Itskari groups to the east is still under some debate. However, all agree that the High Plains sites in Colorado played a unique role in the development and structure of the CPt.