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National Geologic Map Database
Geologic Unit: Sentinel
Map showing publication footprint
  • Usage in publication:
    • Sentinel granodiorite*
  • Modifications:
    • Named
  • Dominant lithology:
    • Granodiorite
  • AAPG geologic province:
    • Sierra Nevada province
Publication:

Calkins, F.C., 1930, The granitic rocks of the Yosemite region: U.S. Geological Survey Professional Paper, 160, p. 120-129, (incl. geologic map, scale 1:125,000)


Summary:

Named for Sentinel Rock [37 deg 43' 43"N, 119 deg 35' 45"W, Mariposa Co, CA], Yosemite National Park. Is oldest unit in Tuolumne intrusive series. Comprises Sentinel Rock and constitutes greater part of both walls of Yosemite Valley from Three Brothers nearly to Royal Arches and from the Fissures east to Glacier Point. Is less uniform in composition than most other intrusive bodies. In western part of zone crossed by Yosemite Valley is relatively light-colored and homogeneous but in eastern part unit is darker and more streaky and contains many dark inclusions. Is in contact with Taft and El Capitan biotite granites which are older. Probably Cretaceous(?) age.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Sentinel granodiorite*
  • Modifications:
    • Geochronologic dating
  • AAPG geologic province:
    • Sierra Nevada province

Map showing publication footprint
  • Usage in publication:
    • Sentinel granodiorite*
  • Modifications:
    • Age modified
  • AAPG geologic province:
    • Sierra Nevada province
Publication:

Calkins, F.C., and Peck, D.L., 1962, Granitic rocks of the Yosemite Valley area, California, IN Geologic guide to the Merced Canyon and Yosemite Valley, California: California Division of Mines and Geology Bulletin, no. 182, p. 17-24.


Summary:

Described as generally medium-dark gray and medium-granular but varies widely. Near contacts with El Capitan tends to be darker and more or less foliated. Plagioclase predominates over potassium feldspar; quartz is inconspicuous; biotite fairly abundant. K-Ar age is 86.4 Ma. [Age of Sentinel Granodiorite changed from Cretaceous(?) to Cretaceous.]

Source: GNU records (USGS DDS-6; Menlo GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Sentinel Granodiorite*
  • Modifications:
    • Geochronologic dating
    • Age modified
  • AAPG geologic province:
    • Sierra Nevada province
Publication:

Kistler, R.W., and Dodge, F.C.W., 1966, Potassium-argon ages of coexisting minerals from pyroxene-bearing granitic rocks in the Sierra Nevada, California: Journal of Geophysical Research, B, Solid Earth and Planets, v. 71, no. 8, p. 2157-2161.


Summary:

Concordant K-Ar age on hornblende, biotite, and orthoclase from same specimen of Sentinel Granodiorite yielded 90 Ma. Age changed from Cretaceous to Late Cretaceous.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Sentinel Granodiorite*
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Sierra Nevada province
Publication:

Bateman, P.C., and Chappell, B.W., 1979, Crystallization, fractionation, and solidification of the Tuolumne intrusive series, Yosemite National Park, California: Geological Society of America Bulletin, v. 90, no. 5, pt. 1, p. 465-482.


Summary:

Western part of Sentinel Granodiorite (Calkins, 1930) "including the rock at Sentinel Rock, the type locality, does not belong to the Tuolumne Intrusive Series" p.466. east part which does belong to series is informally designated as tonalite of Glacier Point.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Sentinel Granodiorite*
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Sierra Nevada province
Publication:

Bateman, P.C., 1992, Plutonism in the central part of the Sierra Nevada batholith, California: U.S. Geological Survey Professional Paper, 1483, 186 p., (incl. geologic map, scale 1:250,000)


Summary:

Included as possible earlier unit of Tuolumne Intrusive Suite. Typical Sentinel Granodiorite resembles Half Dome Granodiorite in being equigranular and containing well-formed crystals of hornblende and biotite and abundant crystals of sphene. Assigned Late Cretaceous age.

Source: GNU records (USGS DDS-6; Menlo GNULEX).


For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

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