1. CHARACTERIZING BOULDER DEPOSITION TO ASSESS ROCK-FALL HAZARD IN UPPER PINES CAMPGROUND, YOSEMITE NATIONAL PARK, CALIFORNIA CORDES, Shaun E., STOCK, Greg M., SCHWAB, Brandon E., and BURKE, Raymond M. Humboldt State University Department of Geology 1 Harpst St, Arcata, CA 95521 shaun.cordes@humboldt.edu

3. Purpose To differentiate between boulders of potential glacial and rock fall origin in order to assess geologic hazards within the Upper Pines campground (UPC) Boulder in Curry Village from 2008 rock fallBoulder in Upper Pines Campground

4. Hypotheses Boulders in Upper Pines Campground could have been transported by two primary processes: (1)glacial ( >15 ka – Last Glacial Maximum) (2)rock-fall (<15 ka) Field and GPS mapping XRF analysis Cosmogenic 10Be exposure ages Methods

6. Mapped Boulders in Upper Pines Campground Angularity Sub Rounded Sub Angular

7. Exposed Volume of Boulders

9. Glacially transported (~12 km) Cathedral Peak Granodiorite. Yosemite Valley was deglaciated 15-17 ka Huber, 1987; Wieczorek and Jager, 1996; Stock and Uhrhammer, 2010

10. Mean: 4.08 m3

12. 96m3 147m3 80m3 76m3 66m3 42m3 Std Dev: 11m3 Volume Relative to Std. Dev.

13. XRF analysis in order to determine source location of largest boulders: sample locations

15. Half Dome granodiorite (Khd) and Glacier Point granodiorite (Kgp) contact

16. Age of Boulders UP-Cosmo-1 10,917 +/- 1043 UP-Cosmo-2 9,607 +/- 954

17. UP-Cosmo-1 UP-Cosmo-2

18. UP-Cosmo-1 Age: 10,917 +/- 1043 XRF: falls within Gray et al. Khd data UP-Cosmo-2 Age: 9,607 +/- 954 XRF: intermediate between Khd/Kgp Contact ~460m above UPC

19. Half Dome granodiorite (Khd) and Glacier Point granodiorite (Kgp) contact

20. Provisional Conclusion Large boulders in the SW corner of the Upper Pines Campground are post-glacial and ~10 ka in age. XRF analysis suggests that UP-Cosmo-2 was near the Khd/Kgp contact ~460m above Upper Pines on Glacier Point Rock fall appears to be the more likely origin for large boulders in the SW corner of the campground.

21. Thank You