Figure 1. Block diagram showing general types of sandand gravel resources in the FRIRP area. Modified fromE.J. Crosby, Landforms in the Boulder-Fort Collins-Greeleyarea, Front Range Urban Corridor, Colorado (USGS Misc.Inv. Series Map 855-H, 1978).

T

Gneiss andigneous rock ofPrecambrian age

Unconsolidatedgravel, sand, and silt

F

A

T

F

T

T

T

H

FTT

H

H

A

T

Terrace

F

TH

A

EXPLANATION

Floodplain and low terraces

High dissected terraceAlluvial fan

Gneiss andigneous rock ofPrecambrian age

Unconsolidatedgravel, sand, and silt

F

A

T

F

T

T

T

H

FTT

H

H

A

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Infrastructure, such asroads, buildings, airports, anddams, is built and maintainedby use of large quantities ofaggregate—sand, gravel, andstone. As urban areas expand,local sources of these re-sources become inaccessible.Other competitive land useshave a higher value than ag-gregate resources. For ex-ample, gravel cannot be mined from under a subdivision. Thefailure to plan for the pro-tection and extraction of infra-structure resources often resultsin increased consumer cost,environmental damage, and anadversarial relationship be-tween the industry and thecommunity.

Natural aggregate is aninfrastructure resource in theFront Range that is producedas sand and gravel or crushedstone. About 80 percent ofColorado's aggregate is sandand gravel, which comes fromfloodplains and terraces alongstream and river valleys, or ashigh dissected terraces and

Government land-usedecisions and environmentalmandates can further precludedevelopment of natural re-sources. If infrastructureresources are to remain econo-mically available, current re-source information must beavailable for use in well-reasoned decisions aboutfuture land use.

During 1973, the Coloradolegislature passed House Bill1529. That act declared thatthe State's natural aggregateresources are essential to theState's economy; the populouscounties of the State face acritical shortage of such re-sources; and such resourcesshould be extracted accordingto a rational plan calculated toavoid waste and cause the leastpractical disruption to the ecol-ogy and to quality of life of thecitizens.

alluvial fans along the mountainfront (fig. 1). About 20 percentof Colorado's aggregate iscrushed stone, which is producedfrom rock quarries commonlylocated in the mountains.

U.S. Department of the InteriorU.S. Geological Survey

USGS Fact Sheet FS–119–98October 1998

FRONT RANGE INFRASTRUCTURE RESOURCES PROJECTAggregate Resources Activities

Goal of Aggregate Resource Activities

FT. COLLINS

DENVER

COLORADOSPRINGS

PUEBLO

EXPLANATION

SAND AND GRAVEL

High

Low

CRUSHED STONE

High

Medium

Low

Very low

Aggregate occurs where nature put it, not necessarilywhere people need it

Geology controls the location and quality of ag-gregate resources. Local aggregate resources may nothave the quality requirements for some uses. Forexample, to be used in a highway, aggregate must behard enough to withstand abrasion from tires, strongenough to support the load of vehicles, and soundenough to withstand freezing and thawing or wettingand drying (fig. 2). Even if adequate supplies of suitable quality ag-gregate resources are available, they may be difficultto obtain because of urban encroachment or otherincompatible land uses. Aggregate is a high-bulk, low-unit-value commodity.Transportation is a significant part of the put-in-placecost of aggregate, and therefore most aggregate oper-ations are located near populated areas. This can putaggregate producers in direct conflict with communitiesthat have their own priorities for use of the land surface,water supply, air, and roads. In some areas the optionsfor places to develop aggregate resources are extremelylimited. Frequently urban growth occurs with neither con-sideration of the resource nor an analysis of the impactof its loss. The old idea that aggregate resources canbe found anywhere is false. New aggregate operationsmay have to be located long distances from the markets.The additional expense of the longer transport ofresources must be passed on to consumers in thecommunity. In addition, longer transport results inhigher fuel consumption, higher emissions, and higherexposure to accidents. As available resources are consumed or preempted,the cost of maintaining or expanding the infrastructureincreases, and the costs are passed on to the public ashigher taxes or in reduced services. To provide for acontinuous supply of reasonably priced, high-qualityaggregate resources, the remaining resources may needto be identified and protected.

The goal of the aggregate resource activity is toprovide industry, decision-makers, and the public withaggregate resource information necessary for makinginformed decisions on future resource availability. This includes information regarding the location,thickness, and quality of aggregate.

Figure 2. Map showing probability of finding high-quality aggregate inFRIRP area.

A reconnaissance map (scale 1:500,000) ofnatural aggregate quality in the Front Range UrbanCorridor has been completed (Langer and others,1997). The Colorado Geological Survey (CGS)undertook mapping of the area's sand and gravelresources during the 1970's. Those maps are sum-marized in "Colorado Geological Survey Atlas ofsand, gravel and quarry aggregate resources,Colorado Front Range Counties." Those aggregateresource maps (1:24,000 scale) have been con-verted to digital format in a cooperative effortbetween the USGS and CGS. Planners and other decision-makers respon-sible for resource management should find bothdigital files just described useful in regional plan-ning and land-use management. Because statutoryregulations, technological capabilities, availablefunding, and land-use priorities vary from place toplace and can be expected to change with time, themaps are designed to provide a resource data basethat will be useful over the years. Being in digitial format, these maps can be used with other digitaldata sets, according to the specific needs of aparticular planning issue. As planning criteria

Descriptive models of gravel deposits for theFront Range Urban Corridor are being directed toward prediction of quality and quantity of unex-plored deposits. Quantity is described in terms ofareal extent, thickness, and volume. Quality isdescribed in terms of areal and vertical distribu-tion of physical parameters such as thickness,clast size, sorting, rock type, proportion of fines,and deleterious materials. Field studies to determine aggregate qualityhave been conducted along the South Platte Riverand the Cache la Poudre River. Seventeen crosssections have been constructed along these tworivers (see examples below) showing details ofthickness and physical properties of sand andgravel resources. Field studies have been con-ducted at 26 sites, and samples from two or threegeologic horizons at each site have been collectedand analyzed. Results of the studies along theSouth Platte River are available in USGS Open-File Reports 98-148-A, B, and C (Lindsey andothers, 1998).

The Front Range Infrastructure Resources Project studies of natural aggregateare focussing on using existing techniques, as well as finding new

approaches to identify and characterize aggregate resources

Digital Maps Available

Report Describes Aggregate Quality

WEST EAST

SOUTHPLATTERIVER

UPPERGRAVEL

MIDDLE GRAVEL

BASAL GRAVEL VE = 40:1

FLOODPLAIN

SOUTH NORTHCACHELA POUDRERIVER

FLOODPLAIN

A A'

B B'

EOLIAN CLAYAND SILT

HOLOCENE GRAVEL

BROADWAY TERRACE

PINEY CREEK TERRACE

5000

4900

4950

FEE

T A

BO

VE

SE

A L

EV

EL

5150

5100

5050

5000

0 1000 2000

0 4000 8000 FEET

METERS

change, the selection of pertinent resource char-acteristics can be adjusted to meet the changingneeds.

1 1/2 inch

3/4 inch

3/8 inch

3/16 inch

<3/16 inch

Satellite and airborneremote sensing data, in com-bination with field, labora-tory, and theoretical studies,help characterize the geology,mineralogy, geomorphology,vegetation, and land-usepatterns associated withcurrent, reclaimed, andpotential aggregate operations.Image processing techniquesare used to develop effectivevisualization for a variety ofraster data sets.

Shallow geophysical techniques are employed tocharacterize deposit thickness, stratigraphy, physicalcharacteristics, and location of the water table. Weconducted field studies in a sand and gravel pit using avariety of geophysical techniques. The most accurate thickness data wereobtained using a tech-nique known as time-domain electro-magnetism. Resultsare described inEllefsen andothers, 1998.

We have completed a study to determine if a cor-relation exists between rock properties estimated bythe Los Angeles degradation test and field tests ofrocks using the Schmidt rebound hammer. Resultsshow that limestone and andesite have an inverse re-lationship between the rebound number and thecorresponding Los Angeles degradation value. Therebound number does not correlate well with granite,gneiss, quartzite, andsandstone. A des-cription of the testmethods and ananalysis of the resultsare available in USGSOpen-File Report98-331 (Davenportand Langer, 1998).

Based on an inventoryand historical review of re-clamation after aggregateextraction in the Front RangeUrban Corridor, and usingother information dealingwith aggregate resources, theprinciples of landscapearchitecture are being appliedto develop methods of assess-ing the visual impact of ex-tracting and reclaimingaggregate. The objective is to identify the geologicand aesthetic factors required to evaluate existing andplanned reclamation and to develop a methodologythat can be used in future management and planning.A description of reclamation-related issues has beenprepared (Arbogast and others, 1998).

Arbogast, B.F., and others, 1998, The human factor in mining reclamation: USGS Open-File Report 98-523.Davenport, J.D., and Langer, W.H., 1998, Estimating Los Angeles degradation value using the Schmidt rebound hammer along the Front Range, Colorado: USGS Open-File Report 98-331.Ellefsen, K.J., and others, 1998, An evaluation of several geophysical methods for characterizing sand and gravel deposits: USGS Open-File Report 98-221.Langer, W.H., and others, 1997, Distribution and quality of potential sources of aggregate, Infrastructure Project Area, Colorado and Wyoming: USGS Open- File Report 97-477.Lindsey, D.A., and others, 1998, Gravel deposits of the South Platte River valley north of Denver, Colorado: USGS Open-File Reports 98-148-A, 98-148-B, and 98-148-C.

W.H. LangerUSGSBox 25046, M.S. 973Denver Federal CenterDenver, CO 80225(303) 236-1249blanger@usgs.gov

D.H. Knepper, Jr.USGSBox 25046, M.S. 964Denver Federal CenterDenver, CO 80225(303) 236-1385dknepper@usgs.gov

Remote Sensing Studies of AggregateResources

Geophysical Studies of Aggregate Resources

References Cited

For More Information Contact

Tool for Characterizing Crushed StoneResources

Environmental Studies of AggregateResources