Located in Douglas County southeast of Chatfield State Park, the Lamb Spring Archaeological Site is the only major site with Paleo-Indian (before 6000 BCE) deposits in the metropolitan Denver area. First excavated in 1961–62, the site contains bison and mammoth bones from the Paleo-Indian period, including evidence of human activity at the site during the Clovis period (11,050–10,750 BCE) or possibly even earlier. The site is now owned by the Archaeological Conservancy and operated by Lamb Spring Archaeological Preserve, which offers free tours and hopes to build an interpretive museum.
About two miles east of the Front Range foothills, Lamb Spring is a natural spring that sits at the head of a draw that drains west to the South Platte River. In 1960 landowner Charles Lamb began to excavate the spring to make a stock pond for his cattle. Before he started, he noticed tusk and bone fragments on the banks of the spring. After uncovering more bones with his backhoe, he got in touch with G. Edward Lewis, a US Geological Survey (USGS) paleontologist in Denver. When Lewis, Glenn Scott, and others from the USGS visited the site, they identified Pleistocene mammal bones as well as Paleo-Indian projectile points.
Recognizing the potential significance of the site, Lewis contacted Waldo Wedel, an archaeologist at the Smithsonian Institution. In 1961–62, Wedel and field assistant George Metcalf excavated the Lamb Spring site with funding from the National Science Foundation. Their work revealed eight geological levels. On the second-lowest level, they found a concentration of bison bones, projectile points, knives, and scrapers. The nature of the bones and artifacts suggested that the remains represented a Paleo-Indian kill site from the Cody complex (8625–7600 BCE), a finding that was confirmed when one of the bones returned a radiocarbon date of about 8000 BCE.
Wedel and Metcalf also uncovered a large concentration of bones in the lowest level, more than five feet below the surface. They found the bones of at least five mammoths, including some that dated to before 11,400 BCE. There were no stone artifacts in this level, but the presence of flaked bones and other features suggested butchering or some other human activity associated with the bones. The site attained enormous significance because it had the potential to yield evidence of human occupation before the Clovis period, the earliest period for which there is archaeological proof of human activity in the Americas.
The Pre-Clovis Question
Later excavations and testing at Lamb Spring focused largely on the question of whether the site contained clear evidence of human activity before the onset of the Clovis period in 11,050 BCE. This work began in earnest in the 1970s after archaeologists developed new concepts of bone processing and bone flaking that allowed them to conclude that some mammoth bones at Lamb Spring were probably modified by humans. This determination resulted in a second excavation of the site in 1980–81, led by Dennis Stanford, Glenn Scott, Russell Graham, and Jim Rancier and funded by the National Geographic Society.
The 1980–81 excavation uncovered several important pieces of evidence. The team found several more mammoths and examined the bones for human modifications. Some evidence suggested human activity: all but one of the long bones (such as femurs) were fractured, while fragile bones (such as ribs) remained intact. In addition, at least three bone cores showed evidence that flakes had been removed. On the other hand, the team found no bone tools or stone tools that would have provided clear evidence of human agency rather than natural processes at work. The team could not say with certainty whether the mammoths had been trampled at the spring or purposefully killed and butchered by humans.
The team also investigated more recent deposits at the site. They found that the Cody period bison kill may have occurred in the summer and involved a full processing and butchering operation after the kill. Above the Cody material they found plenty of Archaic, Plains Woodland, and historic artifacts mixed together, demonstrating that Lamb Spring has been used by the area’s inhabitants from the Paleo-Indian period to the present.
More recently, Steven Holen, then curator of archaeology at the Denver Museum of Nature and Science (DMNS), worked with Dennis Stanford to get more radiocarbon dates for mammoth bones from Lamb Spring that appeared to have been modified by humans. In 2011 the bones returned dates of 11,140 BCE and 11,240 BCE, which are consistent with a Clovis period occupation, as well as 11,620 BCE, which would place humans at Lamb Spring 400–500 years before the traditional start of the Clovis period.
Located just south of Chatfield State Park, the Lamb Spring site became subject to development pressures in the 1990s, after the construction of C-470 and south Denver suburbs such as Highlands Ranch. From the 1970s to the early 1990s, the site was on a 240-acre ranch, but in 1994 the owners divided their land into several smaller parcels and sold it. In order to protect Lamb Spring, in 1995 the Archaeological Conservancy—an Albuquerque-based nonprofit dedicated to preserving significant archaeological sites—worked with Douglas County, the Smithsonian, and DMNS to acquire thirty-five acres around the site. In 2006 the Lamb Spring Archaeological Preserve was formed to operate the site and promote tourism and education there.
In 2012 Douglas County applied for state Regional Tourism Act funding for a project called the Colorado Sports and Prehistoric Park, which would have combined an archaeological museum at Lamb Spring with a ninety-three-acre sports park nearby. The archaeological part of the proposal called for a 38,000-square-foot interpretive museum at the site to help visitors learn about Lamb Spring and understand its significance. In 2013 the proposal was not selected for funding. The developers of Sterling Ranch, a new 3,400-acre community adjacent to Lamb Spring, still plan to build the sports park, but the museum project has been shelved for now. In the meantime, the Lamb Spring Archaeological Preserve has placed informational signs and a cast of an excavated mammoth skull at the site, and it also offers free tours monthly from May through October.