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Geologic Unit: Ladd
Map showing publication footprint
  • Usage in publication:
    • Ladd formation
  • Modifications:
    • First used
    • Biostratigraphic dating
  • Dominant lithology:
    • Shale
    • Siltstone
    • Conglomerate
    • Sandstone
  • AAPG geologic province:
    • Peninsular Ranges province
Publication:

Popenoe, W.P., 1937, Upper Cretaceous Mollusca from southern California: Journal of Paleontology, v. 11, no. 5, p. 379-402.


Summary:

Pg. 380. Ladd formation. Briefly described in "Generalized section of formations in the Santa Ana Mountains, California." Comprises two members, both new (ascending): Baker member, conglomerate grading upward into sandstone, fossiliferous at top, about 200 feet thick; Holz member, sandy shale or siltstone with interbedded arkosic sandstone, fossiliferous in upper half, about 1,500 feet thick. Overlies Cretaceous(?) Trabuco formation; unconformably underlies Williams formation (new). Age is Late Cretaceous based on molluscan fossils described in report.

Source: Publication; GNU records (USGS DDS-6; Menlo GNULEX); US geologic names lexicon (USGS Bull. 1200, p. 2068).


Map showing publication footprint
  • Usage in publication:
    • Ladd formation
  • Modifications:
    • Named
    • Biostratigraphic dating
  • Dominant lithology:
    • Conglomerate
    • Sandstone
    • Shale
  • AAPG geologic province:
    • Peninsular Ranges province
Publication:

Popenoe, W.P., 1942, Upper Cretaceous formations and faunas of southern California: American Association of Petroleum Geologists Bulletin, v. 26, no. 2, p. 162-187. [Available online, with subscription, from AAPG archives: http://www.aapg.org/datasystems or http://search.datapages.com]


Summary:

Type locality designated in region immediately west of mouth of Ladd Canyon, tributary of Silverado Canyon [33 deg 44'51"N, 117 deg 38'23"W, El Toro 7.5' quad, Orange Co, CA]. Ladd formation includes Cretaceous rocks of Santa Ana Mountains lying stratigraphically above Trabuco conglomerate and below Williams formation. Maximum measured thickness is 1700 ft. Divided into (ascending); Baker Canyon member and Holz shale member. [Note that Baker Canyon member was named "Baker member" by Popenoe (1937) and "Baker conglomerate" by Popenoe (1941)]. Age is Late Cretaceous based on molluscan fossils listed and described in report.

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


Map showing publication footprint
  • Usage in publication:
    • Ladd formation*
  • Modifications:
    • Adopted
  • AAPG geologic province:
    • Peninsular Ranges province
Publication:

Woodring, W.P., and Popenoe, W.P., 1945, Paleocene and Eocene stratigraphy of northwestern Santa Ana Mountains, Orange County, California: U.S. Geological Survey Oil and Gas Investigations Chart, OC-12, 1 sheet, scale 1:1,800


Summary:

Stratigraphic chart of northwestern Santa Ana Mountains shows Holz shale member of Ladd formation unconformably underlies Silverado formation (new). Age given as Late Cretaceous.

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


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

Asterisk (*) indicates published by U.S. Geological Survey authors.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).

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