Sand and Gravel Resource Potential Mapping in the Eagle 7 1/2-minute Quadrangle: Applications for Land Use Planning

Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Education, Earth Science



Major Advisor

Monte W. Wilson


The Boise River Valley, Idaho is rich in sand and gravel resources deposited on a sequence of terraces cut episodically by the Boise River as it incised valley-fill sediments of the Western Snake River Plain during the Pleistocene. Communities in the valley have and will continue to experience rapid urban growth. Urbanization increases the demand for construction quality sand and gravel while limiting local access to the resource. Due to their heavy weight and high transportation costs, aggregate products are ideally produced near their end use.

This report integrates the existing geological and land use information pertinent to the sand and gravel resources of the Eagle 7 1/2-minute quadrangle. The report provides geologic descriptions of sand and gravel deposits as well as maps that: 1) identify sand and gravel extraction sites and 2) correlate current land-usage to precluded and potentially extractable sand and gravel resources. The maps will facilitate land use planning with regard to sand and gravel availability for extraction by identifying the extent and quality of the resource relative to urban growth patterns.

The maps are an extension of the Idaho Geological Survey's geologic mapping program initiated in 1986 to interpret the stratigraphy, chronology and geologic history of the Boise 1 x 2 degree quadrangle. The Sand and Gravel Resource Potential Map of the Eagle quadrangle provides a correlation of the previously mapped lithologic units, with emphasis on the Pleistocene and Holocene gravels to the current and potential extraction of sand and gravel resources. This map shows locations of gravel pits on the Whitney Terrace and the Boise River floodplain, the resource potential on the map units, distribution of grain sizes and percentage of stone types in two sites. Analysis of grain sizes reveals a strong bi-modal distribution concentrated on 1 - 3 inch gravel clasts and medium-sized sand. The gravels of the various Boise Valley terraces are texturally indistinguishable from each other indicating episodes of similar incision and deposition throughout the Pleistocene. The gravels are mainly granitic rocks of the Idaho Batholith and porphyritic felsites from the central Idaho mountains.

The Land Use Map Emphasizing Sand and Gravel Resources of the Eagle Quadrangle was generated by modifying the land use and land cover units and designations utilized by the Boise Valley Change Mapping Project of the Idaho Department of Water Resources. The Land Use Map correlates the availability of sand and gravel reserves in the area to general quality characteristics of the resources.

Despite the increased local demand for aggregate resources to support growth in the immediate area, sand and gravel producers and consumers have found it increasingly difficult to obtain access to the resource at a reasonable cost. The factors affecting local availability include environmental issues, urban development, increased land prices, objections from neighbors and incompatibility with community comprehensive planning goals. Obtaining necessary conditional use permits is a prohibitive process.

Unless local land use planning becomes more proactive in identifying and protecting aggregate reserves, competing land uses will continue to endanger resource availability to the detriment of community development and maintenance. The resource maps that were derived from geological maps as part of this study could initiate the designation of "sand and gravel reserves" for prime aggregate resource lands. A description of educational strategies to promote knowledge and understanding of aggregate resources relative to land use issues has been included as an appendix to this study.

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