Jeffrey A. Coe Nikita N. Avdievitch Olivia J. Hoch Jonathan W. Godt Chester A. Ruleman Vince Matthews III 20260106 tabular digital data Golden, Colorado U.S. Geological Survey https://doi.org/10.5066/P13QMK8E As part of an effort by the U.S. Geological Survey (USGS) to better understand topographic and structural conditions that promote slow spreading and sagging of mountain ridges (Varnes and others, 1989), USGS researchers began surveying monitoring points at Bald Eagle ridge in the Sawatch Range of Colorado in 1975 (Radbruch-Hall and others, 1976; Varnes and others, 1990). Bald Eagle ridge forms the southeastern flank of the glaciated Busk Creek valley and is underlain by Mesoproterozoic St. Kevin Granite (Kellogg and others, 2017; Ruleman and others, 2020). Since 1975, surveys of points have continued at roughly decadal intervals, with the most recent survey occurring in 2022 (Table 1). Monitoring point locations on the ridge (Figure 1) were selected to determine if the long-term movement that created multiple uphill-facing scarps, trenches, and a graben on the ridge (features collectively known as sackungen, refer to Figure 1) was still ongoing. Points 1, 2, 3, 4, 6, and K (Figure 1) have been surveyed since 1975. Additional points along a profile line approximately perpendicular to scarps and trenches (points 431 through 438, Figure 1) were added in 1997 and were surveyed in 1997 and subsequent years (1999, 2012, 2013, 2022). Two generations of survey techniques have been used at Bald Eagle ridge, a conventional technique utilizing theodolites and electronic distance measuring devices from 1975 through 1989 (Varnes and others, 1990), and a Global Positioning System (GPS) technique from 1997 through 2022 (refer to Varnes and others, 2000, and Coe and others, 2013). Both the conventional and GPS surveying techniques used point 4 at the top of Bald Eagle ridge (Figure 1) as a fixed, stable point. The stability of point 4 was repeatedly demonstrated using surveys between point 4, and points 6 and K (Figure 1), which showed that the baselines and positions of points 4, 6, and K have remained stable during the monitoring period. Conventional surveys from 1975-1989 required line-of-sight between points. That is, points on the northwest flank of the valley were needed to properly sight points on Bald Eagle ridge. The location of survey positions on the northwest flank of Busk Creek valley and additional details about the conventional methods used for these surveys can be found in Varnes and others (1990). Varnes and others (1990) estimated surveying errors associated with conventional methods to be in the range of 1 to 2 cm. For the GPS surveys from 1997-2022 (refer to Varnes and others, 2000; Coe and others, 2013), measurements were made using static and rapid-static surveying techniques (Van Sickle, 1996). With GPS surveying, direct line of sight between points was not needed, so only points on Bald Eagle ridge (the points shown in Figure 1) were occupied with GPS receivers. The GPS receivers that we used varied over the length of the study. In 1997 and 1999, GPS surveys were done using Ashtech Model Z-12, dual frequency receivers. For surveys from 2012 through 2022, Magellan ProFlex 500 dual frequency receivers were used. The minimum occupation time at each point was 15 minutes, but some occupations were up to 2 hours long, depending on the number and positions of observable satellites, and the availability of people to move and manage the receivers. Our estimate of surveying errors associated with GPS surveying was +/-1.5 cm in horizontal and +/-3.0 cm in vertical. GPS data were post-processed using Ashtech Precise Navigation (PNAV), v. 2.4.00 M software (PNAV, 1997) in 1997 and 1999, and Magellan Survey Solutions software (Survey Solutions, 2010) for 2012 through 2022. Standard errors of computed point positions derived from PNAV and Survey Solutions were less than 1.5 cm in horizontal and 3.0 cm in vertical. Additional details about the GPS methods used for these surveys can be found in Varnes and others (2000). Surveyed point positions from conventional and GPS surveys from 1975-2022 are given in the SurveyData .csv and .xlsx files. Horizontal point positions from conventional surveys are given in North American Datum 1983 (NAD83) Colorado State Plane central zone coordinates. Horizontal positions from GPS surveys are given in the World Geodetic System 1984 (WGS84) and Colorado State Plane central zone coordinates. Vertical point positions for conventional and GPS surveys are given in the North American Vertical Datum 1988 (NAVD88) and as Ellipsoid Heights. Conversion of WGS84 coordinates to the Colorado State Plane coordinate system was done using Ashtech Prism software (Prism, 1997). Conversion of Ellipsoid Heights to NAVD88 elevations was done using the GEOID96 model (refer to https://geodesy.noaa.gov/GEOID/GEOID96/). The WGS84 position of point 4 was initially determined by a static GPS survey of point 4 and two benchmarks with known coordinates provided by the National Geodetic Survey—point "Vail Pass" at Vail Pass and point "V 4" near Leadville. The final WGS84 position of point 4 was determined by least squares adjustment of the triangle formed by the three points. Additional information included in this data release includes the following. Field photos of survey points are included in the SurveyPointPhotos.zip file, organized by the point names and dates of photography. Photos were not available for survey points 435-438. With a few exceptions (as indicated in the photo file names), photos were taken by the first author of this data release. A Google Earth GPSSurveyPointLocations.kml file showing survey point locations, survey point names, and WGS84 coordinates is also included. Table1.jpg provides the survey technique used in each year that surveys were performed. The survey data included in this data release were used in the following interpretive paper: Coe, J.A., Avdievitch, N.N., Allstadt, K.E., Collins, E.A., Jensen, E.K., Hoch, O.J., Schaefer, L.N., Ruleman, C.A., Godt, J.W., Matthews III, V., in review, Sackung at Bald Eagle ridge, central Colorado: an updated interpretation of ridge-spreading movement, structures, and mechanisms from 50 years (1975-2025) of U.S. Geological Survey research: Engineering Geology. Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. References Coe, J.A., Ruleman, C.A., Godt, J.W., Matthews, V., Goehring, B.M., Lucha, P., Deuell, A.E., and Reeves, R.R., 2013, Long-term measurement of ridge-spreading movements (sackungen) at Bald Eagle Mountain, central Colorado [abs.]: Geological Society of America Abstracts with Programs, v. 45, p. 643. https://gsa.confex.com/gsa/2013AM/webprogram/Paper227500.html. Kellogg, K.S., Shroba, R.R., Ruleman, C.A., Bohannon, R.G., McIntosh, W. C., Premo, W.R., Cosca, M.A., Moscati, R.J., and Brandt, T.R., 2017, Geologic map of the upper Arkansas River valley region, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3382, pamphlet 70 p., 2 sheets, scale 1:50,000, https://doi.org/10.3133/sim3382. PNAV, 1997, Precise differential GPS navigation and surveying PNAV software user’s guide: Ashtech, Sunnyvale, California. Prism, 1997, Ashtech Prism software, Ashtech, Sunnyvale, California. Radbruch-Hall, D.H., Varnes, D.J., and Savage, W.Z., 1976, Gravitational spreading of steep- sided ridges (“sackung”) in western United States: International Association for Engineering Geology Bulletin, v. 14, p. 23–35, https://doi.org/10.1007/BF02634754. Ruleman, C.A., Frothingham, M.G., Brandt, T.R., Shaw, C.A., Caffee, M.W., Brugger, K.A., and Goehring, B.M., 2020, Geologic map of the Homestake Reservoir 7.5’ Quadrangle, Lake, Pitkin, Eagle Counties, Colorado: U.S. Geological Survey Scientific Investigations Map 3451, scale 1:24,000, https://doi.org/10.3133/sim3451. Van Sickle, J., 1996, GPS for Land Surveyors: Ann Arbor Press, Chelsea, Michigan, 209 p. Varnes, D.J., Radbruch-Hall, D.H., and Savage, W.Z., 1989, Topographic and structural conditions in areas of gravitational spreading of ridges in the Western United States: U. S. Geological Survey Professional Paper 1496, 32 p. https://pubs.er.usgs.gov/publication/pp1496. Varnes, D.J., Radbruch-Hall, D.H., Varnes, K.L., Smith, W.K., and Savage, W.Z., 1990, Measurement of ridge-spreading movements (sackungen) at Bald Eagle Mountain, Lake County, Colorado, 1975–1989: U. S. Geological Survey Open-File Report 90–543, 13 p. https://pubs.er.usgs.gov/publication/ofr90543. Varnes, D.J., Coe, J.A., Godt, J.W., Savage, W.Z., and Savage, J.E., 2000, Measurement of Colorado, II—Continuation of the 1975–1989 measurements using a Global Positioning System in 1997 and 1999: U.S. Geological Survey Open File Report 00–205, 23 p. https://pubs.er.usgs.gov/publication/ofr00205. We conducted conventional and GPS surveys to monitor ridge-spreading movement at Bald Eagle ridge. 19750601 20221101 publication date Complete As needed -106.47263 -106.41083 39.27107 39.22294 Bald Eagle Mountain and vicinity, Lake County, Colorado ISO 19115 Topic Category biota None Geodetic Global Positioning System GPS Sackung Sackungen Landslide Monitoring Survey theodolite electronic distance measuring USGS Metadata Identifier USGS:687a9a29d4be020457c7b262 None Bald Eagle Mountain Leadville Colorado Sawatch Range Bald Eagle ridge Busk Creek None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Jeffrey A. Coe U.S. Geological Survey Research Geologist Emeritus mailing

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Denver Colorado 80225 USA 303-273-8606 303-273-8600 jcoe@usgs.gov Jeffrey A. Coe, Nikita N. Avdievitch, Olivia J. Hoch, Jonathan W. Godt, Chester A. Ruleman, and Vince Matthews III MS Windows No formal attribute accuracy tests were conducted. No formal logical accuracy tests were conducted. Data set is complete for 1975-2022. No formal positional accuracy tests were conducted. No formal positional accuracy tests were conducted. Two generations of survey techniques have been used at Bald Eagle ridge, a conventional technique utilizing theodolites and electronic distance measuring devices from 1975 through 1989 (Varnes and others, 1990), and a Global Positioning System (GPS) technique from 1997 through 2022 (see Varnes and others, 2000, and Coe and others, 2013). Both the conventional and GPS surveying techniques used point 4 at the top of Bald Eagle ridge (Figure 1) as a fixed, stable point. The stability of 4 was repeatedly demonstrated using surveys between point 4, and points 6 and K (Fig. 1), which showed that the baselines and positions of Points 4, 6, and K have remained stable during the monitoring period. Conventional surveys from 1975–1989 required line-of-sight between points. That is, points on the northwest flank of the valley were needed to properly sight points on Bald Eagle ridge. The location of survey positions on the northwest flank of Busk Creek valley and additional details about the conventional methods used for these surveys can be found in Varnes and others (1990). Varnes and others (1990) estimated surveying errors associated with conventional methods to be in the range of 1 to 2 cm. For the GPS surveys from 1997-2022 (see Varnes et al., 2000; Coe et al., 2013), measurements were made using static and rapid-static surveying techniques (Van Sickle, 1996). With GPS surveying, direct line of sight between points was not needed, so only points on Bald Eagle ridge (the points shown in Figure 1) were occupied with GPS receivers. The GPS receivers that we used varied over the length of the study. In 1997 and 1999, GPS surveys were done using Ashtech Model Z-12, dual frequency receivers. For surveys from 2012 through 2022, Magellan ProFlex 500 dual frequency receivers were used. The minimum occupation time at each point was 15 minutes, but some occupations were up to 2 hours long, depending on the number and positions of observable satellites, and the availability of people to move and manage the receivers. Our estimate of surveying errors associated with GPS surveying was +/-1.5 cm in horizontal and +/-3.0 cm in vertical. GPS data were post-processed using Ashtech Precise Navigation (PNAV), v. 2.4.00 M software (PNAV, 1997) in 1997 and 1999, and Magellan Survey Solutions software (Survey Solutions, 2010) for 2012 through 2022. Standard errors of computed point positions derived from PNAV and Survey Solutions were less than 1.5 cm in horizontal and 3.0 cm in vertical. Additional details about the GPS methods used for these surveys can be found in Varnes and others (2000). References Coe, J.A., Ruleman, C.A., Godt, J.W., Matthews, V., Goehring, B.M., Lucha, P., Deuell, A.E., and Reeves, R.R., 2013, Long-term measurement of ridge-spreading movements (sackungen) at Bald Eagle Mountain, central Colorado [abs.]: Geological Society of America Abstracts with Programs, v. 45, p. 643. https://gsa.confex.com/gsa/2013AM/webprogram/Paper227500.html. PNAV, 1997, Precise differential GPS navigation and surveying PNAV software user’s guide: Ashtech, Sunnyvale, California. Prism, 1997, Ashtech Prism software, Ashtech, Sunnyvale, California. Van Sickle, J., 1996, GPS for Land Surveyors: Ann Arbor Press, Chelsea, Michigan, 209 p. Varnes, D.J., Radbruch-Hall, D.H., Varnes, K.L., Smith, W.K., and Savage, W.Z., 1990, Measurement of ridge-spreading movements (sackungen) at Bald Eagle Mountain, Lake County, Colorado, 1975–1989: U. S. Geological Survey Open-File Report 90–543, 13 p. https://pubs.er.usgs.gov/publication/ofr90543. Varnes, D.J., Coe, J.A., Godt, J.W., Savage, W.Z., and Savage, J.E., 2000, Measurement of Colorado, II—Continuation of the 1975–1989 measurements using a Global Positioning System in 1997 and 1999: U.S. Geological Survey Open File Report 00–205, 23 p. https://pubs.er.usgs.gov/publication/ofr00205. 20251215 Jeffrey A. Coe U.S. Geological Survey, Landslide Hazards Program Research Geologist Emeritus mailing

MS 966, Box 25046

Denver Colorado 80225 USA 303-273-8606 303-273-8600 jcoe@usgs.gov SurveyData.csv Comma Separated Value (CSV) file containing data. Producer Defined Point Name Point Name Producer Defined Point Name Base Point(s) used Base Station Point used Producer Defined NA No Data Producer defined Base Station Point used for surveying Date Surveyed Date that the point was surveyed Producer Defined Date that the point was surveyed, can be specific to the day, or to the year. Baseline Slope Distance (m) Slope distance between the point and the base station Producer Defined NA No Data Producer defined 101.845 1049.538 meters Baseline error (+/- m) Standard error of the slope distance between the point and the base station Producer Defined NA No Data Producer defined 0.006 0.016 meters WGS84 Longitude (West, degrees minutes seconds) WGS84 Longitude Producer Defined NA No Data Producer defined 106 27 15.18151 106 27 54.19479 Degrees, minutes, seconds WGS84 Latitude (North, degrees minutes seconds) WGS84 Latitude Producer Defined NA No Data Producer defined 39 14 06.79151 39 14 43.27627 Degrees minutes seconds Ellipsoid Height (m) Ellipsoid Height Producer Defined 3563.623 3661.359 meters Longitude Error (+/- m) Standard error of Longitude Producer Defined NA No Data Producer defined 0.003 0.006 meters Latitude Error (+/- m) Standard error of Latitude Producer Defined NA No Data Producer defined 0.003 0.007 meters Ellipsoid Height Error (+/- m) Standard error of ellipsoid height Producer Defined NA No Data Producer defined 0.004 0.008 meters Colorado State Plane Easting, NAD83, central zone (m) Colorado State Plane Easting coordinate. The EPSG code for this coordinate system is: EPSG:6427 NAD83(2011)/Colorado Central. The ESRI code is ESRI:103010 NAD 1983 2011 SPCS Colorado Central. Producer Defined 831086.829 832026.38 meters Colorado State Plane Northing, NAD83, central zone (m) Colorado State Plane Northing coordinate. The EPSG code for this coordinate system is: EPSG:6427 NAD83(2011)/Colorado Central. The ESRI code is ESRI:103010 NAD 1983 2011 SPCS Colorado Central. Producer Defined 460863.246 461983.024 meters Height Above Mean Sea Level (NAVD88, m) Height Above Mean Sea Level Producer Defined 3576.496 3674.254 meters GS ScienceBase U.S. Geological Survey mailing address

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Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. Digital Data https://doi.org/10.5066/P13QMK8E None 20260106 GS-HAZ Metadata U.S. Geological Survey physical

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Golden Colorado 80225 USA 303-273-8500 ghsc_metadata@usgs.gov FGDC Biological Data Profile of the Content Standard for Digital Geospatial Metadata FGDC-STD-001.1-1999