Vigil Network Site: Aching Shoulder Slope Near Mitten Rock, New Mexico, U.S.A.
Submitted by: William W. Emmett
U.S. Geological Survey, Washington, D.C. 20242
Aching Shoulder Vigil network Site is located on the Navajo Indian Reservation at Mitten Rock (Mountain), approximately 20 miles southwest of the town of Shiprock in San Juan County, New Mexico. Its coordinates are lat. 36° 36' 19" N., long. 108° 56' 43" W. It is included on the topographic maps published by the U.S. Geological Survey entitled "Ship Rock, N. Mex.," scale 1:62,500 and "Shiprock, N. Mex; Ariz.," scale 1:250,000 (parts of both appear in the folder, figures 1 and 2. The mileage log included in this folder will help enable the observer to find the site.
Aching Shoulder Slope is located at the site of ruins from a Basket Maker Three occupation of early American Indians. The ruins consist mostly of refuse heaps, including broken pottery, and base stones still in place which indicate the outline of walls of early structures. Mittenrock is actually a misnomer by mapmakers from the earlier name Midden Rock, so named because of the refuse heaps. Because of the potential archaeological importance and exploration, some channel sections, hillslope profiles, mass-movement pins and erosion stakes were installed to measure present day rates of processes in the expectation that archaeological studies could provide rates of earlier processes.
A gully at Aching Shoulder Slope separates an igneous slope of rhyolite on the left side of the gully from a sedimentary slope of hornstone on the right. Bedrock crops out frequently, both on the slopes and in the gully channel. The sketch map of figure 3 illustrates prominent outcroppings. Vegetation is sparse and consists of low grasses with maximum densities of five percent. The average elevation is about 5950 feet above sea level and the relief in 1600 feet of surveyed reach is 215 feet. Average precipitation is 8-10 inches per year.
At the time of preparation of this file, four field surveys had been made: August 12-13, 1963, August 8, 1964, August 3, 1965, and August 18, 1968. The 1963 survey consisted of installing ten permanent reference points, each being a four-foot length of 1/2-inch diameter steel rod driven into the ground and protruding about six inches above the ground surface. These reference points are shown on the sketch map of figure 3. A longitudinal profile was surveyed from the watershed divide to a point 1700 feet downslope. Longitudinal profile elevations are listed in table 1. Six of the reference points are end pins for three cross-channel land-surface profiles surveyed at channel stations 0+00, 5+00, and 13+00 as shown on figure 3. These cross-sections are instrumented with ten-inch long steel spikes with a washer under the spike head and driven into the ground at given locations. Values of maximum erosion determined by the distance from the spike head to the washer and deposition by the amount of fill over the washer can be accurately determined along these "nail-washer" lines as long as proper maintenance and surveillance is continued. Channel cross-section data and values of net erosion are tabulated in tables 2, 3, and 4. At the even hundred channel stations, e.g. 2+00, 4+00, etc., three nail-washers as described above were driven into the ground, one in each wall and at the centerline of the gully to measure channel wall slope retreat and scour and fill of the channel bed. Data for these nail and washers are listed in table 5. Two of the reference points are end bench marks for a mass-movement line located on figure 3. The mass-movement line consists of ten-inch long pins driven into the ground and surveyed to determine their position from the line of sight between the two end bench marks. Mass-movement data are listed in table 6. Two slope profiles were surveyed; one on the sedimentary slope and one on the igneous slope at the locations shown on the sketch map of figure 3. They were instrumented with nail-washer pins to determine rates of erosion and the pin locations were accurately measured with a taut steel tape from the top bench marks. Future accurate measurements from the top bench marks can be used to show downslope movement (soil creep) of the shorter pins. Slope profile and erosion data are tabulated in tables 7 and 8. A non-permanent installation of a painted rock line located ten feet downslope of the mass-movement line has been used to show the downslope movement of coarse rock fragments which are very common in the area. Data from the painted rock line are included in table 9. Because of the possible archaeological importance and implications, and the extension to early rates of geomorphic processes, the largest area of ruins and midden were topographically mapped by planetable survey to show land form and ruin locations. This map is shown as figure 4. The surveys of 1964, 1965, and 1969 consisted of resurvey and measurement of existing installations. These data are found in the appropriate table with the initial data.
The file of original data includes black and white and color ground photography (1963-1965) and low-altitude aerial photography (1963). Original data are on file with William W. Emmett, U.S. Geological Survey, Washington, D.C. 20242, U.S.A.