Sand, gravel, and crushed rock rate high among geologic products in
Colorado; more than $27,000,000 worth of these materials were produced
in the state in 1969. Highway and construction activities have brought
recent expansion in the number and size of quarries and gravel pits.
Increasingly, Coloradoans are insisting that quarries and pits be
excavated only where they will not mar the natural beauty of the
landscape, and many old pits are now being filled in. Unfortunately, the
scars left by some quarries—such as that on the Rampart Range near
Colorado Springs—are difficult to erase.
Clay of good quality occurs in Cretaceous deposits in many parts of
Colorado, most frequently in the Dakota or Laramie Formations. In the
area around Golden, the Coors Porcelain Company for many years mined
clay for use in pottery and low temperature ceramic ware. Scars from
this mining can be seen along the mountain front north and south of
Golden, and deep clefts within the town, just west of Colorado School of
Mines, testify to the amounts of clay that have been removed. Colorado
clay is not pure enough to be used in high temperature ceramics, and the
present use for it is in the manufacture of common tiles and bricks.
A recent development in Colorado is the use of Cretaceous Pierre shales
in manufacturing lightweight aggregate for building. The shale is mined
between Golden and Boulder, near Colorado highway 93. In the nearby
plant, it is pulverized and then heated in a large rotating cylinder
until the surface of each particle fuses. Then the particles are quickly
cooled. The resulting product is much like cinder, light in weight and
yet strong. It can be mixed with cement for use in construction work
requiring a great strength-to-weight ratio, or made into concrete
blocks.
[Illustration: Quarrying of Paleozoic limestones and dolomites along the
east flank of the Rampart Range northwest of Colorado Springs has badly
defaced a prominent mountain backdrop. Recent seeding efforts by quarry
operators are returning the exhausted part of the quarry to its original
lightly vegetated condition, and hopefully, as the quarry is depleted,
the scar will disappear. (John Chronic photo)]