History of Bison in the San Luis Valley

The question of the historical presence of bison in the San Luis Valley was one lens through which the Nature Conservancy assessed the possibility of establishing a conservation herd at the Medano-Zapata when they purchased the ranch in the early 2000s. But the available evidence to apply to this question is scant.


In the 1970s, wind began to expose ancient stone tools at a site adjacent to the Zapata. Smithsonian archaeologists determined that these artifacts belonged to a prehistoric people called the Folsom who lived in North America 11,000 years ago. Subsequent excavations taking place over the course of twenty years eventually revealed the presence of an ancient bison kill site. The archaeologists Pegi Jodry and Dennis Stanford surmised from the unearthed relics that a group of Folsom had engaged in a cooperative hunt, killing fifty animals, and had camped at the site for several days as they processed the meat and the hides with their carefully crafted stone tools.

So if bison were present back in 8000 BCE, as multiple other Folson artifact sites around the Valley also show, does that indicate that they’ve historically occupied the area on an ongoing basis? Not necessarily. Jodry’s research also indicates that the Folsom period was characterized by climatic conditions that could have led to the expansion of grassland ecosystems and would have favored radiation in bison populations. Evidence of longer somatic growing seasons, favorable moisture regimes, and an increase in nitrogen availability would have led to abundant, high-quality forage, a resulting rise in bison fertility rates, and an expanding population that would have seen animals move into new areas or spend more time in areas they had only passed through.

Read Jodry’s full paper here.


From the Folsom time 10,00-11,000 years ago up until the colonial time, the historical record on bison is the Valley is very quiet. We know that the Utes moved into the Valley beginning around 1100 CE, and tribes from the south report coming into the Valley to hunt bison and dig for turquoise. An 1853 report from Gwinn Harris Heap contained the following:

“A stream issues from Coochatope Pass and joins the Sahwatch; it is called Coochumpah by the Utahs [Utes], and Rio de los Cibolos by the Mexicans: both names have the same signification – Rive of buffaloes. Coochatope signifies, in the Utah language, Buffalo gate, and the Mexicans have the same name for it, El Puerto de los Cibolos. The pass and creek are so called, from the large herds of these animals which entered Sahwatch and San Luis valleys through this pass, from the Three Parks and Upper Arkansas, before they were destroyed, or the direction of their migration changed, by the constant warfare carried on against them by Indians and Mexicans. A few still remain in the mountains, and are described as very wild and savage.”

Clearly, according to Heap’s understanding, both the Utes and the Mexicans associated the pass with bison, although whether they were reported to move in and out of the Valley seasonally is unclear.


The first known written account of the Valley appears in the journal of Don Diego de Vargas, a Spanish Governor of the Santa Fe territory, in 1694. He came south from Santa Fe and spent six days in the Valley, during which he reported encountering Utes and a herd of 500 bison. After that, the record is strangely silent, apart from a few mentions here and there of a few animals. Subsequent explorers made note of bison herd sightings on the Plains and in the neighboring Wet Mountain Valley, but not once they arrived in the SLV.


So we have to follow two possible lines of thought and answer two difficult questions.

  1. If bison were historical residents of the SLV, why were they not reported in significant numbers following the 17th century?
  2. If bison weren’t full-time occupants of the Valley, perhaps only passing through seasonally, what made this seemingly perfect habitat undesirable to them when there’s evidence that they utilized surrounding areas quite regularly?

To Chris Pague, senior ecologist for the Nature Conservancy and a member of the Zapata conservation bison project from the beginning, the easier scenario to explain is clearly the first. “We have here in the San Luis Valley extremely cold but dry weather, great forage, lots of water that rarely freezes, and very little snow for the most part. That’s prime bison habitat.” Why wouldn’t they have utilized the forage in the Valley?

Pague believes that bison herds disappeared after the first foray into the Valley by the Spanish because of the foreign diseases brought by the newcomers and their cattle. There are reports elsewhere of Old World livestock decimating native bison populations when they first came into contact. “I suspect that’s more likely what happened: the Spanish brought their cattle and the cattle diseases came really reduced populations. That’s probably why later observers only saw a few.”

The current evidence can reasonably support either argument, so we can’t conclusively say whether bison were full-time residents of the Valley or not. But perhaps the point is moot anyway. Ecosystems are constantly in flux, and in the current human and political ecosystem of the Valley, there seems to be a niche for the two thousand animals in our conservation herd, and we enjoy having them around.

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