Today, all that remains of the High Plains in eastern Colorado thrusts westward like a blunt wedge, the point of which rests near Limon (Fig. 2). Westward from Limon, a low divide extends to the foot of the Front Range of the Rocky Mountains, between Denver and Colorado Springs, separating the northeasterly oriented drainage of the Platte river system from the southeasterly oriented system of the Arkansas. At one time, the High Plains extended to the Rocky Mountains, but during the geologic past these two great river systems, which rise in the Rockies and flow eastward across the High Plains of Colorado, have cut broad, deep valleys, largely destroying the Plains which once encroached upon and buried the lower slopes of the mountains. This area of stripped alluvial plains is known as the Colorado Piedmont (Fenneman 1931). On the surface of the High Plains, streams flow eastward down the long, gentle slope toward the Plains border in central Kansas (Fig. 2).

The northwestern border of the High Plains is formed by a low escarpment carved by the northand northeastward-flowing waters of the South Platte River. The southwestern border is formed by another low escarpment cut by the southward- and southeastward-flowing tributaries of the Arkansas River.

The Olsen-Chubbuck Site, properly speaking, consisted of a bone bed contained in an ancient arroyo (Fig. 1). As previously mentioned, this arroyo did not follow the locally normal, north-to-south drainage pattern. Rather, it had its origin near the center of a small catchment basin and flowed eastward through and across the ridge which formed the eastern side of the basin, to debouch on the eastern slope of that ridge (Fig. 7).

The Bone Bed was composed of the skeletons, parts of skeletons, and isolated bones, of about 190 bison (Fig. 1). During our excavations, we recorded a total of 143 skulls. While Olsen and Chubbuck kept no record during their excavations, they estimate that they found about 50 skulls, a figure which appears reasonable in view of the volume they dug and the area in which their excavations were centered. Hence the suggested total of about 190 animals.

Five hundred three bone units were recorded during our 2 seasons of excavation at the Olsen-Chubbuck site (Table 1). A proportionate number of units must also have occurred in that part of the site dug by Olsen and Chubbuck, so that, using the ratio estimated above, somewhere near 670 units probably comprised the total bone bed.

As previously explained (see Recording), each articulated skeleton or segment of a skeleton was recorded as a single unit. In addition, skulls were also recorded as units. We did this because, from early in our first season of excavation, we believed that most, if not all, such articulated segments represented those parts that had been cut off by the Indians during the butchering. That is to say, that the Indians followed a fairly standard procedure in cutting up a bison, and that when the meat had been removed, the bones were discarded, still held together by sinews. We believed that an analysis of such units would provide direct information on the butchering techniques of the Indians, on the selection of choice parts, and perhaps on the use made of the parts. To a large extent, these hypotheses have been validated.

Complete-Animal Units extended along the bottom of the arroyo from Section 5 on the east to Section 22 on the west (Figs. 30A, 3L4). They were not continuous throughout, and occurred with greatest frequency in the deeper eastern part of the arroyo.

Generally speaking, complete-animal units were confined to the inner channel of the arroyo and were thereby constrained to an east or west orientation. However, Units 369,433, 519, 141, and 190 rested at least partly on the upper channel wall.

One group of 8 complete-animal units (290, 324, 327, 366, 367, 369, 398, 433) began in the central part of Section 5 and continued almost to Section 10. In Sections 5 and 6, and again in Section 8, they formed a layer at least 2 deep. No complete-animal units were found in Section 10, but following this gap, another (519) was found in the east end of Section 11. A single complete-animal unit (190) occurred along the Section 16-17 line, and another (93) occupied the bottom of the arroyo from the central part of Section 18 well into Section 19.

The Olsen-Chubbuck Bone Bed (Table 15) produced a total of 4264 non-articulated bones, of which 4007 were found in the eastern part of the site, where nearly every bone was recorded. The figure of 257 bones recorded for the central and western parts of the site is undoubtedly low, although it is indicative of the generally lesser concentration of individual bones as well as articulated units in that part of the arroyo.

It should not be imagined that all of the non-articulated bones represent complete butchering of those bones. No doubt, some of the individual bones became disarticulated through weathering between the butchering phase and final entombment in the bone deposit. This would certainly appear to be the case with such elements as vertebrae, sternal and costal elements, tarsal and carpal bones, phalanges, patellae, sesamoids, and isolated teeth. On the other hand, the butchering process, itself, probably resulted in the disarticulation of certain other kinds of skeletal parts. Removal and breakage of the mandible to get to the tongue, the consequent removal of the hyoid, breakage of the ribs, removal of the legs from the pelvis and the scapula, and removal of the lower leg, are examples of this kind of disarticulation. Even so, some of the leg components, such as femora and tibiae, humeri, radii, and ulnae, may have weathered apart. Some bones may also have been pulled apart by scavengers, but it should be noted in passing that remarkably little evidence was found that the bones had been gnawed by such animals. In any case, it would be difficult to assess completely the role played by weathering, washing, settling, and possible disturbance by scavengers, in the ultimate position of the bones. Even after covering, settling must have continued, and occasional animal burrows must have played a part in the final position of loose bones.

During the Analysis of the bone bed, it became obvious that not only was there a vertical sequence in the emplacing of the groups of units, but that the groups were, for the most part, congregated into locally restricted piles of bone units, unit groups, and non-articulated bones, each more or less separated from other similar piles (Figs. 30I, 31I). Something of this sort had already been noted by Chubbuck in the pattern of the bone outcropping on the surface before the site was excavated, but its full significance was not realized until the bone piles in the undisturbed portions of the site had been discovered. The presence of such piles of bone units suggested not only that a definite pattern had been followed in cutting up the buffalo, but that a number of cooperating social units of some kind had been engaged, each group processing a number of animals and disposing of the rejectamenta as they finished each butchering unit, or that the group successively undertook the butchering of one lot of bison before moving on to the next.

The Olsen-Chubbuck Site is a bison kill. Therefore, it is pertinent to review some of the characteristics of the quarry, for if the archaeologist is to understand the nature and meaning of such kills, he must first understand something about the nature and habits of the bison, particularly the characteristics which made these great beasts susceptible to the techniques of mass slaughter employed by the Indians who hunted them. Moreover, he must understand the methods which the Indians used to kill and butcher the bison, in order to extract the maximum amount of information from his excavations.

If the archaeologist is dealing with prehistoric kills, he must assume that the habits of prehistoric and historic bison were essentially the same, and that the methods of hunting and utilizing them were similar. There can be no doubt that acculturation of the Indian to the use of gun and horse changed, in some cases drastically, the hunting methods of the historic Indians. Yet, the techniques observed by the earliest explorers of interior North America must have remained essentially unchanged over thousands of years. If these assumptions are valid, then we are in a position to comprehend and interpret the evidence recovered in our excavations of bison kills.

Sixty Artifacts and Other Specimens denoting or suggesting human activity were found in and near the Olsen-Chubbuck fossil arroyo and in the bone bed which it contained (Table 20). Forty-seven specimens came either from within the bone bed itself or form the surface among the bones exposed by weathering. One specimen came from the upper, later fill of the arroyo where it had been partly exposed by weathering, and the remaining 12 specimens came from the surface of the site near the arroyo. Along the ridges to the north and west of the arroyo a number of artifacts deriving from later occupation of the area were found.

Twenty-seven of the 47 specimens from the bone bed and the bone-bed surface are projectile points, of which 21 are whole or nearly so, and 6 are tips, midsections, or bases of projectile points.

Those specimens found by Chubbuck and Olsen are designated F-l, F-2, etc. for whole projectile points, and PF-1, PF-2, and so on, for point fragments. All specimens found by the University of Colorado Museum party bear University of Colorado Museum catalog numbers.