The Quarry of the Ancestors is a 199-ha area located 48 km north of Fort McMurray, Alberta. Situated amidst the rolling mixed boreal forest and wetlands of the Muskeg River Valley, it incorporates two expansive surface to near-surface occurrences of Beaver River Silicified Sandstone (BRSS). Despite its name, BRSS is actually an orthoquartzite, a rock type with very high levels of silica and few impurities. Variants of BRSS range from light beige to dark grey in colour and from fine- to coarse-grained in texture, with most examples displaying internal irregularities and weaknesses. However, finer-grained BRSS pieces with few to no flaws can be broken in a predictable fashion, making them well suited to flintknapping, the process of flaking stone into tools by striking it in a controlled fashion. The BRSS occurrences in the Quarry of the Ancestors vary in texture but yield substantial quantities of the fine-grained variant of the rock.
The Precontact residents of northern Alberta and Saskatchewan were clearly aware of BRSS's value for tool making. Their long-term reliance on it is evident in the high density of archaeological sites located in and around the Quarry. These sites typically yield extremely rich assemblages dominated by BRSS tools and flintknapping waste. In fact, archaeologists first became aware of the high level of precontact activity in this area through the discovery of some of these sites during archaeological field studies conducted in association with oil sands development projects during the 1970s and 1980s. The initial efforts to identify the origins of the rock used in the tools from these sites focused on the nearby parts of the Athabasca Valley, where river erosion has exposed the McMurray formation, the geologic stratum that contains both the oil sands and BRSS. This led to identification of a number of possible sources of BRSS, such as the Beaver River Quarry Site. However, the exposures of BRSS at this locality and others along the Athabasca River and its tributaries generally contain the coarse-grained variety of BRSS rather than the fine-grained BRSS that dominates assemblages at archaeological sites in this area.
With further oil sands development during the 1990s and 2000s, the associated archaeological studies expanded to areas east of the Athabasca River, where very high numbers of sites rich in BRSS artifacts continued to be found. In 2003, Nancy Saxberg, a consulting archaeologist who was undertaking a study in advance of proposed development projects in the Muskeg Valley area, recognized that this area not only included large numbers of BRSS-rich sites but also two geological BRSS occurrences yielding fine-grained stone. This material was comparable to the archaeological BRSS variants common in sites throughout the region, strongly suggesting that this was a primary source of this material. Additional archaeological studies in the Muskeg Valley area have continued to reveal the long, rich record of precontact BRSS use, leading to an initiative to protect this unique archaeological locality by declaring it a provincial historical resource (see Historic site).
These previous studies, as well as ongoing archaeological work occurring in advance of expanding oil sands extraction, have recovered projectile point types that suggest that precontact use of BRSS was heaviest between 9800 and 5500 years ago. Confirmation from radiocarbon dates is being sought but is extremely difficult to get, because the acidic soil in this region destroys all organic artifacts suitable for radiocarbon dating. As a result, there is some ongoing debate about the reliability of assigning dates by comparing points from sites in and around the Quarry to specimens of known age and distinctive size and shape from adjacent regions, such as the Northern Plains. Nonetheless, it appears likely that the Quarry was used by some of the region's earliest precontact residents. They appear to have advanced into this landscape relatively soon after it was exposed by the retreating Laurentide ice sheet, at a time when the outpouring of glacial meltwater from nearby glacial Lake Agassiz was still reshaping the local landforms. This makes the rich archaeological record in and around the Quarry of the Ancestors an invaluable resource, not just for understanding precontact activity in a region once thought to have been sparsely occupied, but also for understanding how this region was first peopled.