The Tools of Time

How do we know what the landscape of the Colorado Plateau looked like a hundred or a thousand or ten thousand years ago? The answers will depend in part on the questions we ask, and the questions we ask will determine the tools that we use.

The Colorado Plateau is famous for its archaeological treasures, and archaeological tools have been the primary means of uncovering the layers of material culture and stratigraphy of the region. Southwest archaeology is not, however, the focus of this website, as the subject is competently reviewed elsewhere (e.g. Sipapu: Yhe Anasazi Emergence Into the Cyber World). We have included a section on archaeoastronomy, since the Ancient Puebloans themselves used the procession of heavenly objects to guide them in their own agricultural land-use.

Biological tools are used to describe materials that are organic in origin. Packrats (Neotoma) are nature's premier curator. Neotoma produce middens when they clean their dens and nests and produce debris piles functionally similar to mine tailings. Paleoecologists search middens and other sites for fossils, from which much can be learned about past biotic communities. Fossils may include plant materials, the remains of amphibians, reptiles, arthropods, birds, or mammals, or the dung of any of these animals.

Fossil pollen is preserved in lake and cave deposits, and provides a more generalized view of past vegetation, as most pollen grains can be identified only to plant family or genus. Pollen analysis is ideal for understanding the composition of wind-pollinated vegetation communities such as woodlands and forests.

Fossils and geological deposits are almost meaningless unless they are placed within a timeframe--a chronology. The two most widely used chronological tools on the Colorado Plateau are radiocarbon dating and dendrochronology, the study of tree rings. Dendrochronology  reveals local climatic and hydrologic histories stretching back in excess of 2000 years. Trees also record fire scars which cause a sequence of overlapping wounds. These reveal not only a history of frequent, low intensity surface fires in the forests of the Colorado Plateau prior to Euro-American settlement, but an ecologically significant linkage between fire and the Southern Oscillation (El Niño/ La Niña). Recently, a series of other dating techniques, some quite sophisticated, are coming into use in research on the Plateau.

Geological tools are used to examine inorganic materials. Geomorphology is the study of changes in the form or shape of the earth’s surface, and while it may suggest only the ancient past, the Colorado Plateau's long history of volcanism (volcanic activity) extends even to the present day. Lava flows, lava dams, ash falls, and even spectacular volcanic structures such as Sunset Crater have had impacts on human and vegetative life at many different temporal and spatial scales. Glacial features such as moraines and glacial striations are abundant in areas glaciated today, so their presence in some of the highlands of the Colorado Plateau suggests that in the past glaciers once flowed down a few of the region's mountains, and are an important indicator of climatic change.

Materials on the surface of the earth accumulate and erode over time with changes in environmental conditions and events. In any undisturbed deposit the oldest layers are normally located at the lowest level. Accordingly, it is presumed that the remains of each succeeding generation are left on the debris of the last. Quaternary stratigraphy is the study of those remains, and may yield information on, for example, the hydroclimatology of extreme events.

Historical tools include land survey data stretching back to the eighteenth century. These are of great value in characterizing vegetation at the point in time when each survey was made, and include descriptions of forest type, locations of streams, and other landscape features. Oral and written histories of the Colorado Plateau, such as Major John Wesley Powell’s seminal "A Report Upon Lands of the Arid Regions of the United States," have provided environmental historians with detailed descriptions of the region prior to Anglo settlement.

Photography is over one hundred years old, and some of the earliest images of the Colorado Plateau have been rephotographed by contemporary land-use historians. Repeat photography has been particularly valuable in documenting the impacts of grazing, fire suppression, and woodland expansion.

Streamflow records from stream gaging of more than 50 years are now common. They are revealing climatic episodes of wetter or dryer than normal and lasting longer than a decade. Analysts are beginning to be able to use this data to determine whether these changes are natural or a result of human activities.

For the recent past, a pair of powerful geographical tools are available. Remote sensing is the primary business of the U.S. Geological Survey (USGS) Earth Resources Observation Systems (EROS) Data Center, also known as the EDC. Besides handling data from several series of satellites, the EDC archives more than 8 million photographs taken from airplanes. Data from any of the above research tools can be entered into a GIS, or Geographical Information System. GIS is increasingly becoming as essential a tool in land-use and land cover research as the trowel, the camera, or the computer.