The Sentinel - Boulder standing near the start of the Apex Trail. The dark, upper part, is gneiss, the result of relatively fast cooling.  The bottom part, closer to granite, is the result of slower cooling, which allowed the growth of larger grains and crystals.

Gneiss Gallery - The Apex Trail (Idaho Springs Batholith)

The Apex and Gregory Wagon Road

By Jack Barkstrom

Apex Trail Gneiss

If travelers along the Apex and Gregory Wagon Road were looking for anything along the trail, it would have been the burnt quartz John Gregory had found, a sign that they were in gold country.  They would have seen quartz, as well as granite and mica, but not in the quantities, or of a type close to what had been found around Black Hawk and Central City.

What would have attracted the eye were the boulders and outcrops of red and grey rock.  Most of it was gneiss.  In contrast to the dramatic colors. which would have attracted attention, the age, 1.7 billion years, would have been incomprehensible to the travelers.  Most of the rock was seeing the light of day for the first time, give or take a few hundred thousand years.

The gneiss along the Apex trail exhibits a wide variety of patterns.  Distinct parallel, and wide, bands can be seen in some of the rock.  The twists, turns, and swirls in other exposures indicate the high temperature and molten, even soupy, state it was in before it cooled.  The presence of granite and the long pegmatitic intrusions into or between other rock suggest that there were pockets or layers of differing temperature and pressure which acted to create the varying patterns seen today on the trail.