Stop 8.  Old Pikes Peak Quarry

Depart Parking Area and Drive to Homestead Parking Area on West Edge of Park

 Hike Down the Trail Just West of the Homestead Parking Area

The Old Pikes Peak Quarry is located on the western edge of the State Park, but within the Park’s limits.  Dolomites of the Dunleith Formation, lower Galena Group, are exposed in the quarry.  Although the collecting of rocks within a State Park is strictly prohibited, Park Ranger Jim Farnsworth has graciously granted permission for GIS Field Trip participants to collect at this site during the field trip.  Should you choose to return to this quarry at a later date, you must obtain permission to collect samples from the Park Ranger.

The photograph to the right shows the trail head from the Homestead Parking Area to the Old Pikes Peak Quarry

.

The uppermost bedrock strata represented in Pikes Peak State Park belong to the Dunleith Formation of the lower Galena Group, an widespread formation regionally characterized by limestone and dolomite strata, cherty in part.  This old quarry area is one of the best places to look at these strata in the park.  Along the highway below the quarry is a roadcut section that displays strata of the underlying Decorah Formation.  The roadcut section includes part of the same strata exposed at nearby McGregor Quarry (see Stop description), and general features will not be repeated here.

  The quarry floor is actually developed on a limestone bed in the uppermost part of the Ion Member of the Decorah Formation.  A shallow excavation below the quarry floor displays the subjacent green-gray shales which characterize much of the Decorah.  This interval includes large stony bryozoans, similar to the Prasopora-bearing units at the McGregor Quarry.  Unfortunately, the contact between the Decorah and Dunleith formations is not clearly visible at the Pikes Peak Quarry, but it lies a very short distance above the quarry floor within a thin covered interval at the base of the quarry wall.

The Dunleith Formation at this quarry is subdivided into three members:  1) a lower interval, argillaceous in part, comprised of calcitic dolomite and dolomitic limestone (Beecher Member); 2) a middle interval of vuggy dolomite with numerous nodules of white to gray chert (the Eagle Point Member); and 3) an upper unit of vuggy dolomite, generally free of chert (Fairplay Member).  These strata are dolomitized and recrystallized to varying degrees, which serves to clearly separate them from the shales and limestones of the underlying Decorah Formation.

The Beecher Member differs from overlying Dunleith units at this quarry in containing dolomitic limestones, part slightly argillaceous.  Fossils are poorly preserved by recognizable in this interval.  Irregular hardground surfaces are identified in the member, marking episodes of nondeposition on the seafloor.  The Eagle Point Member is distinguished by an abundance of chert nodules, usually seen as light colored cherty bands within the vuggy dolomites.  Two intervals with enigmatic receptaculitid fossils are also seen in this member.  Strata of the Fairplay Member generally lack chert at this quarry, except at its very base.  These upper dolomite ledges are, in part, porous and highly weathered, although a prominent zone of common receptaculitid fossils is seen here (unit 18).  Higher strata of the Dunleith Formation are found within Pikes Peak State Park, and overlying Dunleith units are identified in the upland water well near the south entrance.  These include the Mortimer (cherty dolomitic limestone), Rivoli (cherty dolomitic limestone and dolomite), and Sherwood (non-cherty dolomitic limestone) members.

GRAPHIC SECTION OF THE STRATA EXPOSED AT THE PIKES PEAK QUARRY AREA click on section to view higher resolution image for printing click on section to view higher resolution image for printing

Click here for written description of the rock section
at the Pikes Peak Quarry

To get to Stop 9 we will have to
drive north on Hwy 341

Depart Parking Area and Drive North (turn right) about 3/4 miles,  then turn into McGregor Quarry, just beyond the western limits of Pikes Peak State Park

The turn off Highway 340 into the McGregor Quarry is easy to miss, so keep alert.  The drive into the quarry is gated and locked, but McGregor city officials have given us access for the field trip.