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The latest issue of Survey Notes is here!

Our latest issue of Survey Notes is here!
Find articles on the Tooele 30’x 60′ quadrangle geologic map and practical uses of geologic maps, along with our regular featured columns.

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Holocene Surface-Faulting Earthquakes at the Spring Lake and North Creek Sites on the Wasatch Fault Zone: Evidence for Complex rupture of the Nephi Segment

Holocene Surface-Faulting Earthquakes at the Spring Lake and North Creek Sites on the Wasatch Fault Zone: Evidence for Complex rupture of the Nephi Segment

By: Christopher B. DuRoss, Michael D. Hylland, Adam I. Hiscock, Stephen F. Personius, Richard W. Briggs, Ryan D. Gold, Gregg S. Beukelman, Greg N. McDonald, Ben A. Erickson, Adam P. McKean, Stephen J. Angster, Roselyn King, Anthony J. Crone, and Shannon A. Mahan

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This 44-page report presents new data from the Spring Lake and North Creek trench sites on the Nephi segment of the Wasatch fault zone. We use paleoseismic data from these sites to refine Holocene earthquake chronologies for the northern and southern strands of the segment, calculate earthquake recurrence and fault slip rates, and assess whether the strands rupture independently or synchronously in large earthquakes. At the Spring Lake site, at least five to seven earthquakes occurred since ~13.1 ka, yielding a mean Holocene recurrence of ~1.2–1.5 kyr; at the North Creek site, at least five earthquakes occurred since ~4.7 ka, yielding a mean recurrence ~1.1–1.3 kyr. We integrate these results with previous paleoseismic data for the segment, discuss the timing and recurrence of large Nephi segment earthquakes, and evaluate possible models of surface-fault rupture involving the two fault strands.

Water Salinity Study for the Southern San Pitch Drainage System in Sanpete County, Utah

Water Salinity Study for the Southern San Pitch Drainage System in Sanpete County, Utah
By: Janae Wallace, J. Lucy Jordan, Christian Hardwick, and Hugh Hurlow

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This project determines the sources and extent of salinity in the lower San Pitch River drainage and adjoining Gunnison Irrigation Company canal system in southern Sanpete Valley using data we acquired over two field seasons documenting water quality and quantity along different reaches within the San Pitch River and Twelvemile Creek as well as nearby canals and springs. We use geologic mapping and geophysical techniques (TEM) to isolate and identify regions in the subsurface that likely have an influence on river salinity. The data collected for this study provide information necessary to make targeted management decisions to reduce salinity and provide for a sustainable supply of acceptable/suitable quality irrigation water for the GIC and its water users. Overall, our maps emphasize areas of higher and lower salinity sources and show calculated salt load to the San Pitch River.