Abstract

Considerable local and international demand exists for beach sand from southern Monterey Bay, California. Uses of this specialty sand include filtration, sandblasting, foundry, and surface finishes. Approximately 90% is medium- to coarse-grained sand and granule gravel. Quartz, feldspar, and granitic rock fragments total 82 % by volume, which results in a Mohs hardness of about 6.5 and a high temperature of fusion. Sand in the 0.7 to 1.0 mm range has an average Folk roundness of 3.2 (subrounded) and is well polished. Its amber color, valuable for architectural purposes, is a product of iron-staining on the surfaces of 17% of the grains. Knowledge of the sand provenance provides a geologic basis for calculation of a new sand budget or re-evaluation of available budgets to determine the degree to which beach sand mining contributes to coastal erosion in southern Monterey Bay. Comparisons were made of grain-size distributions, lithologic compositions, and grain surface attributes to determine the provenance of medium- to coarse-grained beach sand. Landward migration of relict or modern offshore surface sand and wave erosion of pre-Flandrian and Flandrian coastal dunes are important sources, and there may be significant contributions from the Salinas River during flooding. Contributions by southward littoral transport across the head of Monterey Canyon, northward littoral transport from the Monterey Peninsula, offshore winds, and landward migration from offshore exposures of the Monterey, Paso Robles, and Aromas Formations are negligible.

First Page Preview

First page PDF preview
You do not currently have access to this article.