Geology, coastal geomorphology, and soils of eastern Santa Cruz Island (Limuw), Channel Islands National Park, California, USA

By: , and 
Edited by: Nicholas Van Buer and Joshua J. Schwartz

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Abstract

This one-day field trip explores northeastern Santa Cruz Island (Limuw, in native Chumash), a part of Channel Islands National Park, USA. The geomorphology of eastern Santa Cruz Island has been controlled largely by active tectonics and sea-level fluctuations. The bedrock is Miocene volcanic rock overlain by Miocene shale and siltstone. The island has experienced Quaternary uplift, perhaps due to movement along an offshore thrust fault. Smaller faults are exposed in sea cliffs and have displaced Miocene rocks. Superimposed upon island uplift, there have been Quaternary sea-level fluctuations from interglacial-glacial climate changes. Interglacial high-sea stands are recorded as marine terraces. The last major interglacial period, ~120,000 years ago, left only small remnants of marine terraces. Most evidence of this high-sea stand was eroded away in the Holocene. However, a prominent marine terrace is preserved at 75–120 m above sea level. Some fossil mollusks from the deposits of this terrace, probably reworked, have given ages as old as Pliocene, but most yield ages of 2.6–2.0 Ma. The age and elevation of this terrace indicate a very low rate of tectonic uplift, similar to nearby Anacapa Island. A low uplift rate explains the absence or scarcity of younger terraces, including that of the last interglacial period. Low stands of sea (glacial periods) exposed the insular shelf, rich in carbonate skeletal sand. During glacial periods, these sands were entrained by the wind, deposited as dunes on marine terraces, and cemented into eolianite. Clay-rich Vertisols with silt mantles have developed on eolianites and terraces of the island, partly from in situ weathering, but also from inputs of Mojave Desert dust during Santa Ana wind events. This guide includes stops at Scorpion Anchorage, Cavern Point, and Potato Harbor. It provides insights into the bedrock, coastal geomorphology, fossiliferous marine terraces, eolianite, Vertisols, and the three formations on eastern Santa Cruz Island: the Santa Cruz Island Volcanics, the Monterey Formation, and the Potato Harbor Formation.

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Publication type Book chapter
Publication Subtype Book Chapter
Title Geology, coastal geomorphology, and soils of eastern Santa Cruz Island (Limuw), Channel Islands National Park, California, USA
DOI 10.1130/2024.0070(05)
Volume 70
Year Published 2024
Language English
Publisher Geological Society of America
Contributing office(s) Geosciences and Environmental Change Science Center
Description 42 p.
Larger Work Type Book
Larger Work Subtype Monograph
Larger Work Title From coastal geomorphology to magmatism: Guides to GSA connects 2024 Field trips in southern California and beyond
First page 83
Last page 124
Country United States
State California
Other Geospatial Channel Islands National Park, Santa Cruz Island (Limuw)
Additional publication details