Figure 1. Block diagram showing general types of sand

and gravel resources in the FRIRP area. Modified from

E.J. Crosby, Landforms in the Boulder-Fort Collins-Greeley

area, Front Range Urban Corridor, Colorado (USGS Misc.

Inv. Series Map 855-H, 1978).

T

Gneiss and

igneous rock of

Precambrian age

Unconsolidated

gravel, sand, and silt

F

A

T

F

T

T

T

H

F T

T

H

H

A

T

Terrace

F

T

H

A

EXPLANATION

Floodplain and

 low terraces

High dissected

 terrace

Alluvial fan

Gneiss and

igneous rock of

Precambrian age

Unconsolidated

gravel, sand, and silt

F

A

T

F

T

T

T

H

F T

T

H

H

A

Printed on recycled paper

 Infrastructure, such as

roads, buildings, airports, and

dams, is built and maintained

by use of large quantities of

aggregate—sand, gravel, and

stone. As urban areas expand,

local sources of these resources become inaccessible.

Other competitive land uses

have a higher value than aggregate resources. For example, gravel cannot be mined 

from under a subdivision. The

failure to plan for the protection and extraction of infrastructure resources often results

in increased consumer cost,

environmental damage, and an

adversarial relationship between the industry and the

community. 

 Natural aggregate is an

infrastructure resource in the

Front Range that is produced

as sand and gravel or crushed

stone. About 80 percent of

Colorado's aggregate is sand

and gravel, which comes from

floodplains and terraces along

stream and river valleys, or as

high dissected terraces and

 Government land-use

decisions and environmental

mandates can further preclude

development of natural resources. If infrastructure

resources are to remain economically available, current resource information must be

available for use in wellreasoned decisions about

future land use.

 During 1973, the Colorado

legislature passed House Bill

1529. That act declared that

the State's natural aggregate

resources are essential to the

State's economy; the populous

counties of the State face a

critical shortage of such resources; and such resources

should be extracted according

to a rational plan calculated to

avoid waste and cause the least

practical disruption to the ecology and to quality of life of the

citizens.

alluvial fans along the mountain

front (fig. 1). About 20 percent

of Colorado's aggregate is

crushed stone, which is produced

from rock quarries commonly

located in the mountains. 

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–119–98

October 1998

FRONT RANGE INFRASTRUCTURE RESOURCES PROJECT

Aggregate Resources Activities
Goal of Aggregate Resource Activities

FT. COLLINS

DENVER

COLORADO

SPRINGS

PUEBLO

EXPLANATION

SAND AND GRAVEL

High

Low

CRUSHED STONE

High

Medium

Low

Very low

Aggregate occurs where nature put it, not necessarily

where people need it

 Geology controls the location and quality of aggregate resources. Local aggregate resources may not

have the quality requirements for some uses. For

example, to be used in a highway, aggregate must be

hard enough to withstand abrasion from tires, strong

enough to support the load of vehicles, and sound

enough to withstand freezing and thawing or wetting

and drying (fig. 2).

 Even if adequate supplies of suitable quality aggregate resources are available, they may be difficult

to obtain because of urban encroachment or other

incompatible land uses.

 Aggregate is a high-bulk, low-unit-value commodity.

Transportation is a significant part of the put-in-place

cost of aggregate, and therefore most aggregate operations are located near populated areas. This can put

aggregate producers in direct conflict with communities

that have their own priorities for use of the land surface,

water supply, air, and roads. In some areas the options

for places to develop aggregate resources are extremely

limited.

 Frequently urban growth occurs with neither consideration of the resource nor an analysis of the impact

of its loss. The old idea that aggregate resources can

be found anywhere is false. New aggregate operations

may have to be located long distances from the markets.

The additional expense of the longer transport of

resources must be passed on to consumers in the

community. In addition, longer transport results in

higher fuel consumption, higher emissions, and higher

exposure to accidents.

 As available resources are consumed or preempted,

the cost of maintaining or expanding the infrastructure

increases, and the costs are passed on to the public as

higher taxes or in reduced services. To provide for a

continuous supply of reasonably priced, high-quality

aggregate resources, the remaining resources may need

to be identified and protected.

 The goal of the aggregate resource activity is to

provide industry, decision-makers, and the public with

aggregate resource information necessary for making

informed 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 in

FRIRP area.
 A reconnaissance map (scale 1:500,000) of

natural aggregate quality in the Front Range Urban

Corridor has been completed (Langer and others,

1997). The Colorado Geological Survey (CGS)

undertook mapping of the area's sand and gravel

resources during the 1970's. Those maps are summarized in "Colorado Geological Survey Atlas of

sand, gravel and quarry aggregate resources,

Colorado Front Range Counties." Those aggregate

resource maps (1:24,000 scale) have been converted to digital format in a cooperative effort

between the USGS and CGS.

 Planners and other decision-makers responsible for resource management should find both

digital files just described useful in regional planning and land-use management. Because statutory

regulations, technological capabilities, available

funding, and land-use priorities vary from place to

place and can be expected to change with time, the

maps are designed to provide a resource data base

that will be useful over the years. Being in digitial 

format, these maps can be used with other digital

data sets, according to the specific needs of a

particular planning issue. As planning criteria

 Descriptive models of gravel deposits for the

Front Range Urban Corridor are being directed 

toward prediction of quality and quantity of unexplored deposits. Quantity is described in terms of

areal extent, thickness, and volume. Quality is

described in terms of areal and vertical distribution of physical parameters such as thickness,

clast size, sorting, rock type, proportion of fines,

and deleterious materials.

 Field studies to determine aggregate quality

have been conducted along the South Platte River

and the Cache la Poudre River. Seventeen cross

sections have been constructed along these two

rivers (see examples below) showing details of

thickness and physical properties of sand and

gravel resources. Field studies have been conducted at 26 sites, and samples from two or three

geologic horizons at each site have been collected

and analyzed. Results of the studies along the

South Platte River are available in USGS OpenFile Reports 98-148-A, B, and C (Lindsey and

others, 1998). 

The Front Range Infrastructure Resources Project studies of natural aggregate

are 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

SOUTH

PLATTE

RIVER

UPPER

GRAVEL

MIDDLE GRAVEL

BASAL GRAVEL VE = 40:1

FLOODPLAIN

SOUTH NORTH

CACHE

LA POUDRE

RIVER

FLOODPLAIN

A A'

B B'

EOLIAN CLAY

AND SILT

HOLOCENE GRAVEL

BROADWAY

 TERRACE

PINEY CREEK

 TERRACE

5000

4900

4950

FEET ABOVE SEA LEVEL

5150

5100

5050

5000

0 1000 2000

0 4000 8000 FEET

METERS

change, the selection of pertinent resource characteristics can be adjusted to meet the changing

needs.

1 1/2 inch

3/4 inch

3/8 inch

3/16 inch

<3/16 inch
 Satellite and airborne

remote sensing data, in combination with field, laboratory, and theoretical studies,

help characterize the geology,

mineralogy, geomorphology,

vegetation, and land-use

patterns associated with

current, reclaimed, and

potential aggregate operations.

Image processing techniques

are used to develop effective

visualization for a variety of

raster data sets.

 Shallow geophysical techniques are employed to

characterize deposit thickness, stratigraphy, physical

characteristics, and location of the water table. We

conducted field studies in a sand and gravel pit using a

variety of geophysical techniques. The most accurate 

thickness data were

obtained using a technique known as timedomain electromagnetism. Results

are described in

Ellefsen and

others, 1998.

 We have completed a study to determine if a correlation exists between rock properties estimated by

the Los Angeles degradation test and field tests of

rocks using the Schmidt rebound hammer. Results

show that limestone and andesite have an inverse relationship between the rebound number and the

corresponding Los Angeles degradation value. The

rebound number does not correlate well with granite,

gneiss, quartzite, and

sandstone. A description of the test

methods and an

analysis of the results

are available in USGS

Open-File Report

98-331 (Davenport

and Langer, 1998).

 Based on an inventory

and historical review of reclamation after aggregate

extraction in the Front Range

Urban Corridor, and using

other information dealing

with aggregate resources, the

principles of landscape

architecture are being applied

to develop methods of assessing the visual impact of extracting and reclaiming

aggregate. The objective is to identify the geologic

and aesthetic factors required to evaluate existing and

planned reclamation and to develop a methodology

that can be used in future management and planning.

A description of reclamation-related issues has been

prepared (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. Langer

USGS

Box 25046, M.S. 973

Denver Federal Center

Denver, CO 80225

(303) 236-1249

blanger@usgs.gov

D.H. Knepper, Jr.

USGS

Box 25046, M.S. 964

Denver Federal Center

Denver, CO 80225

(303) 236-1385

dknepper@usgs.gov

Remote Sensing Studies of Aggregate

Resources

Geophysical Studies of Aggregate Resources

References Cited

For More Information Contact

Tool for Characterizing Crushed Stone

Resources

Environmental Studies of Aggregate

Resources