Julia Matheny and Dr. Matthew Bekker, Geography
Montezuma Canyon, of San Juan County, Utah has a long and rich history of human occupation with land use by various peoples. The Anasazi occupied the area from 200 to 1300 A.D., at which time the area was abandoned. Euroamerican pioneers came into the canyon in the 1880’s and introduced domestic cattle, which promoted grazing into the area. Since the time of Euroamerican settlement, the landscape of Montezuma Canyon has undergone dramatic changes due to erosion. Grazing, along with various other land uses involved in ranching and farming, have been suggested as possible causes of erosion, loss of viable soils and ground water (Womack and Schumm 1977). This has led to the abandonment of small scale farming and the endangerment of Anasazi ruins located in the canyon.
My study involved the dating of erosion terraces in one portion of Montezuma canyon. These terraces have developed due to erosional forces. Although erosion is a natural process, it is our belief that erosion has increased in the canyon since Euroamerican occupation. By dating cottonwood trees located on the terraces we hoped to show an increase in erosion since that time. These terraces can be dated by coring cottonwood trees located on the terraces. The germination and growth of cottonwood trees, Populus fremontii, are linked to the course and movement of a channel of water (Everitt 1968). Cottonwoods will only germinate when in proximity to a body of water. Many of the older cottonwoods located in upper to mid-Montezuma Canyon, are no longer growing next to Montezuma Creek but are located on erosion terraces, some of which are 35 to 40 feet above the present creek bed. This information tells us that severe erosion has been taking place in the canyon during historic and recent times.
The portion of the canyon in which I performed my study contains two erosion terraces where cottonwood trees are presently growing. Below the two erosion terraces at the bottom of the canyon and several feet away, Montezuma Creek flows. We were able to determine the height and position of the erosion terraces and Montezuma Creek by making use of a GPS unit. Unfortunately the GPS reading for the height of Montezuma Creek was lost and an additional trip to obtain the reading was not possible. The lower terrace (the terrace closest to the present course of the creek) is located a little more than a foot above the creek. The upper terrace (the terrace farthest from the creek) is nearly eight feet above the first terrace.
As our results reveal, a significant change in terrace height tells us that since the time that these cottonwoods established, erosional forces have affected the flow of Montezuma Creek, forcing it to alter its course. By coring and dating the cottonwood trees located on these terraces we can determine the ages of the trees and the relative ages of the terraces on which they are located. We are then able to determine when Montezuma Creek flowed at the height of the terraces.
We cored 7 trees and took 13 core samples from these trees. 6 cottonwood trees were located on the lower terrace. All of these trees germinated and established in the 1980s within a few years of each other. This means that Montezuma creek, which is about 10 feet away and 1 foot below the trees on the lower terrace, was flowing by these trees in the 1980’s.
Only one cottonwood tree was located on the upper terrace, which is 8 feet above the lower terrace. Unfortunately, this tree was old and in bad condition and it was not possible to take a complete core to the center of the tree because of rot. We took 3 cores of this tree but we were only able to take the date back to 1959. This tree is likely much older than this date implies, therefore it was not possible to produce a relative age for the upper terrace, we only know that it is older than 1959. Thus we see that the upper terrace has undergone serious erosion by its relative height to the lower terrace, but we are unable to say when Montezuma creek flowed at the upper terrace level.
This project helped to reveal significant changes taking place in Montezuma canyon; however, there is still much work to be done to determine the extent of erosion in the canyon. A much larger scale project would be necessary to truly show the effects of erosion in Montezuma canyon.