An Underground Particle Physics Lab in Idaho Springs, Colorado

Honestly, I probably wouldn't be blogging this article if it weren't discussing a new major physics experiment facility less than an hour away from my home. It is even closer to the University of Colorado at Boulder, and the Colorado School of Mines, both of which have high quality advanced physics programs staffed by elite physics PhD professors. CU-Boulder has been the home institution of quite a few Nobel prize winners.

The problem is that cosmic rays that include muons, and other surface bound sources of background noise, prevent scientists from conducting precision studies of low-energy muon production in ordinary university laboratories on the surface.

The basic strategy at this laboratory is to remove that background noise by putting the detection instruments deep in a mine originally dug for gold mining (the high school in Idaho Spring's somewhat titillating mascot as a result of this legacy of gold mining is the "gold diggers"). Initial calibrating tests show that the cosmic muon flux deep in the mine that was detected matches what the designers of the experiment expected to a reasonable degree. 

This laboratory setting provides a relatively inexpensive space to do research without background noise from cosmic and Earth-bound sources of contaminating charged particles, which is important for high precision measurements that could be done in a university laboratory but for their background interference. It reduces background noise 700-fold despite providing shielding only equivalent to a depth of about 415 meters.

There are only five underground laboratories of this kind in North America and only about a dozen in the entire world, not including CURIE, and they are in high demand.

We present the characterization of cosmogenic muon backgrounds for the Colorado Underground Research Institute (CURIE), located in the Edgar Experimental Mine (EEM) in Idaho Springs, Colorado. 

The CURIE facility at the EEM offers a versatile shallow underground environment, with accessible horizontal tunnel access and stable rock formations ideal for low-background physics experiments. We have measured the total underground muon flux in two locations, Site 0 and Site 1, yielding values of ϕ = 0.246 ± 0.020 sys. ± 0.012 stat. and 0.239 ± 0.025 sys. ± 0.010 stat. μ/m2/s, respectively. 

We have utilized GEANT4 and PROPOSAL Monte Carlo simulations with Daemonflux and MUTE to model the muon flux at both sites, as well as an additional future location. We find good agreement between measurement and simulations, demonstrating the first instance of this computational framework being successfully used for depths < 1 km.w.e. The measured underground flux corresponds to a factor of 700 reduction compared to the sea level flux. 

Additionally, we present a new depth-intensity relationship to normalize the mountain overburden to an equivalent flat depth, enabling direct comparison with other underground facilities. We report an average equivalent vertical depth of 0.415 ± 0.027 km.w.e. Based on our measurements, this work highlights the facility's capability for hosting low-background experiments, addressing the demand for shallow underground research spaces.

Dakota K. Keblbeck, Eric Mayotte, Uwe Greife, Kyle G. Leach, Wouter Van De Pontseele, "Cosmogenic Muon Background Characterization for the Colorado Underground Research Institute (CURIE)" arXiv:2411.01626 (November 3, 2024).

There Was A Megadrought In The Colorado River Basin In The 100s CE

Colorado is currently in a 1200 year drought (the worst since 800 CE). But, in the 100s CE, around the time that the Roman Empire was at its peak and Christianity was in a formative period, there was a far more severe drought than the current one in the Colorado River basin or the one experienced around 800 CE.

The drought of ca. 800 CE was probably a decisive factor in the collapse of the Anasazi a.k.a. Ancient Puebloan culture. It predated by about two centuries the arrival of the Navajo and Apache people in the American Southwest from what is now Southern central Canada. It also coincided with the arrival of the Thule ancestors of the modern Eskimo people of Alaska and Canada in Western Alaska from Siberia which was a major push factor behind the southern mass migration of the ancestors of the Navajo and Apache people.

The Colorado River is in an extremely severe drought and has been for the last 22 years. To better understand this drought, researchers looked at the drought history within the Colorado River Basin. Previous studies have gone back 1,200 years, but this paper goes back 2,000 years. The findings, using paleo hydrology, show that there was an even more severe drought in the Colorado River Basin in the second century. . . . . The research finds that compared to the current 22-year drought in the Colorado River, with only 84% of the average water flow, the water flow during a 22-year period in the second century was much lower, just 68% of the average water flow.

From Science Daily citing Subhrendu Gangopadhyay, et al., 'Tree Rings Reveal Unmatched 2nd Century Drought in the Colorado River Basin." 49(11) Geophysical Research Letters (June 9, 2022). DOI: 10.1029/2022GL098781

The abstract and other prefatory materials from the paper are as follows:

Abstract

The ongoing 22-year drought in the Upper Colorado River Basin (UCRB) has been extremely severe, even in the context of the longest available tree-ring reconstruction of annual flow at Lees Ferry, Arizona, dating back to 762 CE. 

While many southwestern drought assessments have been limited to the past 1,200 years, longer paleorecords of moisture variability do exist for the UCRB. Here, gridded drought-atlas data in the UCRB domain along with naturalized streamflow data from the instrumental period (1906–2021) are used in a K-nearest neighbor nonparametric algorithm to develop a streamflow reconstruction for the Lees Ferry gage starting in 1 CE. 

The reconstruction reveals a second-century drought unmatched in severity by the current drought or by well-documented medieval period droughts in the UCRB. Although data are sparse, analysis of individual long tree-ring records and other paleoclimatic data also support the occurrence of an exceptional second-century drought. 

Key Points

A new tree-ring based ensemble streamflow reconstruction spanning the last two millennia was developed for the Colorado River

The new reconstruction reveals a second-century drought unmatched in severity by any past droughts in the Upper Colorado River Basin

The ongoing 22-year period of low Colorado River streamflow is a rare event, but is not the most severe drought in the past 2,000 years

Plain Language Summary

The Colorado River drought we currently are experiencing is severe in the context of the 116-year gage record (1906–2021), but how severe is it in a long-term context? 

Existing tree-ring based reconstructions of Colorado River streamflow have suggested that the 22-year period 2000–2021 could be the worst drought in the southwestern United States in 1,200 years. The purpose of this study is to extend the Colorado River reconstruction back 2,000 years and to evaluate the current drought in a long-term context. 

We find that an even more extreme drought occurred and persisted over much of the second century. Data are sparse this far back in time, but evidence from both tree-ring data and paleoclimate data from lakes, bogs, and caves supports the existence and severity of this drought in the context of the last two millennia. 

Additional work is needed to learn more about this drought and its causes, but we now know that drought more persistent than even the well-documented medieval period droughts occurred in the past, expanding our understanding of the range of natural climate variability.

 The body text goes on to explain that:

Other paleoclimatic data provide additional support for second-century drought (e.g., Routson et al., 2021; Shuman et al., 2018). A collection of 37 non-tree-ring hydroclimate records (e.g., pollen, diatoms, etc.) was assessed for evidence of the second-century drought. Resolution and age control limit these records' ability to faithfully record events that occurred within multidecadal timescales. However, non-tree-ring hydroclimate records are useful because they are not limited by detrending and short segment lengths inherent in tree-ring chronologies (Cook et al., 1995). This collection of lower resolution records shows dry conditions occurred during the second century over a spatial domain broadly consistent with the tree-ring based evidence. Furthermore, these records show a gradual pattern toward wetter conditions over the last two millennia, with the driest conditions occurring in the early portion of the first millennium, coincident with the second century. This period also coincides with the higher frequency of longer and more severe droughts over the first millennium in the tree-ring records.

Local Cultural and Historical Context

In part due to my thinner understanding of North American prehistory, some of which is my own fault, and some of which is due to a lack of a good comprehensive chronology in academia itself, I struggle to recall anything terribly significant or notable going on in the American Southwest in that time period, that would overshadow the well known climate impacts of the less severe drought that was experienced six or seven centuries later. 

This drought coincides with the time period in the region is known among archaeologists as the Late Basketmaker II era (from 50 CE to 500 CE), which is "a cultural period of Ancient Pueblo People when people began living in pit-houses, raised maize and squash, and were proficient basket makers and weavers. They also hunted game and gathered wild foods, such as pinyon nuts." 

There isn't a lot that is known about these people, but what is known is summarized as follows:

Communities

The primary dwellings of this era were round or circular pit-houses that were built on open land and partially below the ground surface. The entrance to the house faced east or south. Logs and rocks were often used for the dwellings foundation. The building materials for the walls could include stacked logs, jacal or poles and brush. In the center of the dwelling was a fire pit.

Some early people built their dwellings within the natural protection of rock shelters, especially during the beginning of this period. 

Agriculture

The Basketmaker II people raised maize and squash, the first people of the northern American southwest to do so, which required them to be located near sources of water and good soil. Carbon isotope analysis of bones of Archaic people compared to Basketmakers indicates that the Basketmakers' diet was rich in maize.

Manos and metates were used to grind maize and other foods. Food was stored below ground in storage cists, often lined with slabs of stone.

Material goods

Excavated items from this period include: 

* good quality, tightly woven baskets

* woven yucca bags, sandals and blankets

* robes and blankets made of feather and fur

* stone projectile points, scrapers and knives

* atlatl and throwing spears (the main tools for hunting)

* bone stitching awls, whistles, and gaming pieces

* cord made from yucca and cedar bark

* oval-shaped cradles

* stone pipes

About AD 200, the middle of this period, there was some experimentation with a crude form of brown pottery.

Wikipedia's Timeline of North American Prehistory provides the following entries between and around these two droughts in this part of North America also sometimes called Oasisamerica (all dates CE except as noted in the first two entries):

• 500–1 BCE: Basketmaker phase of early Ancestral Pueblo culture begins in the American Southwest.
• 300 BCE: Mogollon people, possibly descended from the Cochise tradition, appear in southeast Arizona and southwest New Mexico.

• 200–1450: Hohokam cultures flourish in Arizona and north Mexico
• 400: Cultivation of maize (corn) begins in the American Southeastern Woodlands and soon reaches the Northeastern Woodlands. Originally domesticated in Mesoamerica, maize transforms the Eastern Agricultural Complex.
• 400: Ancestral Pueblo peoples of the American Southwest weave extraordinarily long nets for trapping small animals and make yucca fibers into large sacks and bags.
• 500: Late Basketmaker II Era phase of Ancestral Pueblo culture diminishes in the American Southwest.
• 700: Basketmaker III Era of the American Southwest evolve into the early Pueblo culture.
• 755±65 – 890±65: likely dates of the Blythe Geoglyphs being sculpted by ancestral Quechan and Mojave peoples in the Colorado Desert, California
• 700–800: Ancestral Pueblo people of the American Southwest or Oasisamerica transition from pit houses to multi-story adobe and stone apartments called pueblos.
• 875: Patayan people begin farming along the Colorado River valley in western Arizona and eastern California.
• 900: Ancestral Pueblo culture dominates much of the American Southwest.
• 900: American Southwestern tribes trade with Indigenous peoples of Mexico to obtain copper bells cast through the lost-wax technique.
• 915 (exact date): Construction begins at Pueblo Bonito, the largest Ancestral Pueblo Great House.
• 900–1150: Pueblo II Era in the American Southwest
• 1000–1200: Acoma Pueblo and Old Oraibi are established, and become the oldest continuously inhabited communities in the United States
• 1100: Pueblo Bonito in Chaco Canyon reaches apex in size at 800 rooms
• 1100: Hohokam culture reaches apex in present-day Arizona
• 1150–1350: Pueblo III Era in the American Southwest

There is a two centuries gap in the prehistory of the American Southwest that includes the time period of this megadrought. 

The archaeological record would be consistent with the hypothesis that human civilization basically ended as a result of this megadrought in the American Southwest starting about 0 CE and restarted again with Hohokam culture around 200 CE when the Colorado River basin had recovered again. Or, it could simply be that the archaeological record as filtered through to me through secondary sources is just incomplete or inaccurate.

This excerpt from the Wikipedia Hohokam article describes the early phase of this culture and suggests that a 200 CE date may be a bit early for it:

Pioneer/Formative period (AD 1–750)

As farmers of corn and beans, early Hohokam founded a series of small villages along the middle Gila River. The communities were located near arable land, and dry farming was common early in this period. Water wells, usually less than 10 feet (3 m) deep, were dug for domestic water supplies. Early Hohokam homes were built of branches that were bent, covered with twigs or reeds and heavily applied mud, and other available materials.

Crop, agricultural skill, and cultural refinements increased between AD 300 and 500 as the Hohokam acquired a new group of cultivated plants, presumably from trade with peoples in the area of modern Mexico. These acquisitions included cotton, tepary bean, sieva and jack beans, cushaw and warty squash, and southwestern pigweed. Agave species had been gathered for food and fiber for thousands of years by southwestern peoples, and around 600, the Hohokam began cultivating agave, particularly Agave murpheyi ("Hohokam agave"), on large areas of rocky, dry ground. Agave became a major food source for the Hohokam to augment the food grown in irrigated areas.  

Engineering improved access to river water and the inhabitants excavated canals for irrigation. 

Evidence of trade networks include turquoise, shells from the Gulf of California, and parrot bones from central Mexico. 

Seeds and grains were prepared on stone manos and metates. 

Ceramics appeared shortly before AD 300, with pots of unembellished brown used for storage and cooking, and as containers for cremated remains. Materials produced for ritual use included fired clay human and animal figures and incense burners.

Weird Trees In North America Were Made That Way To Send A Message

This practice of shaping trees to communicate information was common throughout pre-Columbian North America. Please point out examples of this practice outside of North America in the comments if you are aware of any.

To mark trails, river crossings, or important sites such as Pikes Peak in Colorado, Native Americans would bend young trees into shapes that were not found in nature, such as right angles. Once moulded, saplings would retain these unusual shapes throughout their lives. 

 From here. 

Photo by Bob Falcone of the Colorado Springs Independent. 

John Anderson pointing out a Ute Indian burial tree. The section coming up from the ground represents birth, the horizontal section represents a walk through life and the section rising up to the sky represents returning to the heavens (death). (Thank you in advance Bob Falcone and Cara DeGette for honoring this claim of fair use for scientific and educational purposes without profit).

[M]any CMTs in Park and Teller Counties point toward Pikes Peak which held spiritual significance to Utes — others point towards what we now refer to as Ute Pass. And some of the trees point towards constellations while others show relation to seasonal solstices and equinoxes.

From the Colorado Springs Independent citing John Wesley Anderson, a retired engineer, former El Paso County Sheriff, and researcher working closely with current Ute Tribal leaders (one of the main tribes in Colorado today and at the earliest attested post-Columbian times).

Pike's Peak, Colorado via Wikipedia.

A spiral juniper tree at Deadhorse Point State Park near Moab, Utah. Stock Images. 

Zaleski State Forest, Ohio. Knowandtell CC BY-SA 3.0

Jasper, Georgia, USA. Wasrts CC BY-SA 3.0

Ancient Puebloan Migration May Have Involved A Radical New Social Organization

In the late 1200s CE, the Ancient Puebloans a.k.a. Anasazi precipitously left their complex of villages in Southwest Colorado in the vicinity of Mesa Verde.

Many of them ended up in the Tewa Valley of New Mexico to the South through which the Rio Grande River runs, something that new research has confirmed with evidence like the genetics of turkey bones, which is expanded upon in an article for the High Country News.

In part, this was driven by climate. 

But, archaeological evidence and the oral tradition also suggests that there may have been a radical change in the social, political and economic organization of the migrants. 

The Mesa Verde civilization was economically organized by household and was riddled with intracommunity strife that may have been along the lines of disputes between the haves and the have nots in the society. 

But, late in Mesa Verde's development, a new more community oriented society was developed around a community about six miles away now called "Yucca House" in a national monument, that put a public square rather than family specific kivas at the center of the community and was more egalitarian and communal. This late site near Mesa Verde appears to have provided the social model for the migrants communities new homes in the Teva Valley that consciously rejected much of the old material culture and architectural style of the Mesa Verde civilization that failed when placed under stress.

Grassroots Astronomy In 13th Century Colorado

Most of the ancient Puebloan sites in the American Southwest have architectural features designed to serve as observatories for the movements of the sun during the course of the year, something common to many early agricultural societies. These are generally limited to public spaces and the homes of chiefs and high priests.

But, in the Hovenweep complex of ruins, along the Colorado-Utah border, from about 1166 CE to 1277 CE, a different phenomena was observed. There, ordinary people' homes also has astronomical observation features (e.g. architectural arrangements that light up a special marker on the day of the winter solstice).

Zuni ethnographic reports from the 19th century indicate that ordinary people used these because they didn't trust the Sun priests who kept the official astronomical and calendar records to get it right.

Teofilo at Gambler's House explains his take on this phenomena, although he doesn't have a pat answer.

Did the Chacoans trust their sun priests more than the later people of Hovenweep and Zuni? 

I think they just might have, and this brings me back to another theory I’ve proposed: that the rise of Chaco to a position of regional dominance in the tenth and eleventh centuries AD may have been associated with Chacoan elites’ control of new and ritually important astronomical practices. The astronomical alignments at Chaco appear to be the earliest known ones in at least the northern Southwest, and possibly the Southwest as a whole, and it’s possible that the development (or acquisition) of observation techniques that allowed Chaco’s leaders to demonstrate unprecedented powers of prediction fueled their rise. As long as those powers seemed to hold, they may have been able to keep close control over knowledge of their techniques, or the common people may simply have not thought to question them. 

But Hovenweep, with its apparently more “democratic” distribution of astronomical knowledge, dates to only slightly later than Chaco. So what happened in between?

It’s hard to say, and this is one of the enduring mysteries of Chaco, but this period (roughly the middle decades of the twelfth century) does appear to have been a time of great change throughout the northern Southwest, with the ultimate result being the loss of Chaco’s regional influence, although the canyon itself wasn’t completely abandoned until the whole region was at the end of the thirteenth century. There were some major droughts that occurred during this period, which seem to coincide with some of the cultural changes, so maybe the Chacoan elites’ esoteric calendrical knowledge no longer seemed to have the control over rain and fertility that they had claimed, and people began to trust them less and to try to do their own observations too. Or maybe there was a more general spread of astronomical knowledge that undermined Chaco’s influence even if its power didn’t appear to fail. It’s very hard to tell exactly what happened, but the patterns are intriguing.

Information about the parallel practices in the "Old World" aren't terribly informative, because they took place thousands of years earlier than they did in the New World. Historians had a brief window in which they could interview Zuni Sun priests before cultural change completely wiped away all memory of the old ways, while many of the old ways associate with this kind of solar astronomy were long gone by the time that a meaningful written historical record had emerged in Eurasia.