Global Positioning System survey data from 2014-2022 on the West Salt Creek rock avalanche deposit, Mesa County, Colorado

The West Salt Creek rock avalanche (refer to Figure 1 for location, .pdf and .jpg files are provided) occurred on May 25, 2014, and filled the West Salt Creek valley with a hummocky deposit that ranged up to ~38 m thick (White and others, 2015; Coe and others, 2016). The central core of this deposit continued to move for at least one hour after other parts of the deposit had stopped moving (refer to Figure 7 in Coe and others, 2016). The deposit contained boulders of basalt and Green River Formation shale in a finer-grained matrix (Lewis and others, 2023). Since deposition, shale boulders on the surface of the deposit have been gradually disintegrating (slaking).  As the shale boulders break apart, the surface of the overall deposit is gradually beginning to look like it was emplaced as a slow-moving earth flow. If the central part of the rock avalanche deposit were to move again (either rapidly or slowly), it could threaten gas wells and infrastructure located downslope from the deposit.
 
To monitor the central core of the deposit for movement, beginning in November, 2014, we gradually installed and periodically surveyed points at 12 positions along the length of the central core (Figure 2, .pdf and .jpg files). The timing of point installations and surveys is contained in Table 1 (.pdf and .jpg files). In addition to Figure 2, survey point locations are provided in a Google Earth file (WestSaltGPSSurveyPointLocations.kml). All survey points are rock bolts in basalt boulders located within the central core of the deposit. Photos of survey points are included in a zipped file (SurveyPointPhotos.zip). Photos were available for all points except MP5. We did not install survey points on the rock-slide slump block at the head of the rock avalanche because it was being monitored with automated GPS stations installed and maintained by the Mesa County Public Works Division.
 
On May 27, 2016, an outburst flow from a sag pond at the head of the 2014 rock avalanche incised and eroded rock-avalanche material, and deposited debris-flow and hyperconcentrated-flow deposits, both on and within the rock-avalanche deposit, and for another ~8 km downstream in the Salt Creek valley (Coe and others, 2026). This flow destroyed some of the survey points (MP5 and MP8, refer to Table 1). Additional survey points (Points MP1 and MP2, Table 1) were destroyed by grading for trail building. We replaced some of the destroyed points and added an “a” to their point names to distinguish them from the original points (refer to Table 1).      
 
All surveys were conducted using rapid static Global Positioning System (GPS) surveying techniques (refer to Van Sickle, 1996) and Magellan ProFlex 500 dual frequency receivers. For rapid static surveying we used point Base (Table 1 and Figure 2) near a gas well pad adjacent to the rock avalanche deposit as a base station. Our estimate of surveying errors associated with rapid static GPS surveying was +/-1.5 cm in horizontal and +/-3.0 cm in vertical. The WGS84 position of point Base was determined by a static GPS survey from Mesa County survey point FKPT(1008) (Table 1 and Figure 2). WGS84 coordinates and ellipsoid height for FKPT(1008) were provided by Frank Kochevar, surveyor for the Mesa County Public Works Division.
   
GPS data were post-processed using Magellan GNSS Solutions software (GNSS Solutions, 2010). Standard errors of computed point positions derived from GNSS Solutions software were less than +/-1.5 cm in horizontal and +/-3.0 cm in vertical. Surveyed point positions from GPS surveys are given in the WestSaltGPSSurveyData .csv and .xlsx files. Horizontal positions are given in the World Geodetic System 1984 (WGS84) and Universal Transverse Mercator (UTM) zone 13 coordinates. Vertical point positions are given as Ellipsoid Heights and in the North American Vertical Datum 1988 (NAVD88). Conversion of WGS84 coordinates to UTM coordinates was done using Magellan GNSS Solutions software (GNSS Solutions, 2010). Conversion of Ellipsoid Heights to NAVD88 elevations was done using the GEOID12A model (refer to https://geodesy.noaa.gov/GEOID/GEOID12A/). 
 
The most recent survey data contained in this data release were from August 4, 2022. Our results through that date were consistent with settling and compaction of the core of the rock avalanche deposit. We saw no evidence for en masse movement of the deposit.

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References

Coe, J.A., Baum, R.L., Allstadt, K.E., Kochevar, B.F., Jr., Schmitt, R.G., Morgan, M.L., White, J.L., Stratton, B.T., Hayashi, T.A., and Kean, J.W., 2016, Rock-avalanche dynamics revealed by large-scale field mapping and seismic signals at a highly mobile avalanche in the West Salt Creek valley, western Colorado: Geosphere, v. 12, no. 2, p. 607–631, https://doi.org/10.1130/GES01265.1.

Coe, J.A., Baxstrom, K.W., Jensen, E.K., Leidelmeijer, J.A., Leung, M.T., 2026, Incision and deposits resulting from outburst flow from the sag pond at the West Salt Creek rock avalanche, western Colorado: U.S. Geological Survey data release, https://doi.org/10.5066/P1TAKEUJ.

GNSS Solutions, 2010, Magellan Navigation, Inc. Professional Office software, v. 3.0.

Lewis, A.C., Baum, R.L., and Coe, J.A., 2023, Distribution of large boulders on the deposit of the West Salt Creek rock avalanche, western Colorado: U.S. Geological Survey Data Report 1178, 6 p., https://doi.org/10.3133/dr1178.

Van Sickle, J., 1996, GPS for Land Surveyors: Ann Arbor Press, Chelsea, Michigan, 209 p.

White, J.L., Morgan, M.L., and Berry, K.A., 2015, The West Salt Creek Landslide: a catastrophic rockslide and rock/debris avalanche in Mesa County: Colorado Geological Survey Bulletin 55, https://doi.org/10.58783/cgs.b55.isrw2611.