Imagine standing on the rim of a tall escarpment overlooking a valley that stretches from horizon to horizon. Across the valley the ground slopes steadily up and away, while behind rise jagged ranges of peaks and mesas veiled by monsoon clouds. Torrents of storm water and sediment wash down from these highlands and pour over the valley rim. Heaps of broken rock and layers of mud, sand, and pebbles spread out across the basin below. From time to time, the low rumble of an earthquake echoes across the flatland, as the weight of accumulating sediments flexes deep bedrock to the point of breaking. This process has been going on for millions of years.

Looking closer at the valley floor hundreds of feet below, ribbons of steam rise up from scattered hot springs, and a fringe of green marshland surrounds a corridor of meandering river channels and shallow lakes. Within these wetlands, primitive fish, gigantic toothy amphibians, armor-plated reptiles, and small, agile dinosaurs thrive. It's two hundred million years ago on the cusp of the Triassic and Jurassic geologic periods, and we're standing at the edge of a crack in the earth along which the supercontinent Pangaea is slowly being pulled apart. In today's terms, we're looking southeast from the current location of Hershey, Pennsylvania.

Now, let’s dive down the steep fault scarp and follow it underground. At about four miles below the surface of the floodplain we reach the future level of Hersheypark Drive. Another four or five miles below that lie the oldest layers of the sediments that have been washing in from the neighboring highlands. Thirty to fifty miles deeper still, under conditions of intense heat and pressure, blobs of viscous, molten rock are rising up from earth's mantle. Some of this magma, rich in iron, calcium, and magnesium, makes it to the surface to form volcanoes and lava flows. Larger volumes of magma, however, remain trapped below the surface, filling cracks and intruding between flat layers of sedimentary rock. As these magma bodies slowly cool and harden, their elemental ingredients combine to form interlocking mineral crystals of light-colored feldspar and dark-colored pyroxene. When fully solidified, the dense gray rock is called diabase.

Origins: Diabase

A Climbers’ Guide to Deep Time

During the two-hundred million years since this dynamic landscape existed, a lot has happened. The sun and its family of planets has made one full rotation around the Milky Way galaxy. Pangaea continued to fall apart as a larger, more active volcanic rift valley to the east was flooded by seawater creating the Atlantic Ocean. Most of the prehistoric creatures living in the floodplain went extinct - except for the dinosaurs, who went on to greater things for a while. The Pangaean mountains and valleys were then worn down flat by erosion, uplifted, and then etched away again, several times. This process of uplift and erosion continues to the present day. The thick sheets of diabase that solidified miles underground had their tilted edges exposed at the surface. Erosion has left them to form higher ground, rising above lowlands composed of the ancient rift basin's soft sandstones and shales.

Finally, during only the last three million years, where conditions were just right, the exposed bedrock was shattered by the repeated freezing and thawing of multiple ice ages, to form Pennsylvania's diabase bouldering areas at Governor Stable, Mount Gretna, and Haycock Mountain, along with the sport climbing walls of Birdsboro Quarry.