By just walking along a trail in Maine you may not realize it but, you’re hiking over a landscape that was shaped by time. Huge forces created the features lying beneath your feet and in the views surrounding you, whether you’re in Acadia, the canyon of Gulf Hagas or on the summit of Mount Katahdin.

Oceans rose, volcanic offshore islands collided with the continent, then the oceans receded, the land rose, glaciers advanced and scraped off what was left. The evidence of all this cataclysmic activity is everywhere, if you know where to look.

It all started around 400 million years ago when Maine and the East Coast were under water. Volcanic islands off the existing coast were moving toward a collision with the continent. As they drifted, sediments were washed from the volcano’s slopes into the sea. The sediments formed into shale under the pressure and weight of increasing amounts of silt.

Then, the shale under the sea was heated by magma from below and formed slate. On a hike in Gulf Hagas near Greenville the clues to this activity and subsequent events is clear in the vertical cliffs that form the gorge.

Once the slate cooled and formed bedrock under the ocean, the volcanoes collided with the North American continent, forcing the slate upward. The vertical lines in the 120-foot high walls of the canyon attest to the fact that this rock was once horizontal, then pushed up. The rim trail that runs for a little more than five miles, round trip, along the top of the cliffs is rugged and made up of this slate.

After the collision with the mainland, what remained of the volcanoes formed the foundation for some of the western mountains of Maine, such as Saddleback and Bigelow. Then came another big event, a second chain of volcanic islands followed the first, after 100 million years or so, straight into the continent. All this colliding of rock into rock created friction and friction creates heat. Temperatures were so high that solid rock melted and became liquid magma. Where sediments were washed from the continent and flowed into the sea, then collided, they formed granite domes of magma, since most of the continental shelf is granite bedrock.

Mount Desert Island is one of those domes of molten granite that was formed by heat under the ocean from the collision. If you hike along the trails in Acadia National Park you are walking on granite that was once liquid magma, undersea, then cooled and hardened into the rock that formed the mountains.

Now, fast-forward from a few hundred million years ago to 12,000 years ago, fairly recent in geologic time. This time was when the massive continental glacier known as the Laurentine Ice Shield covered the entire state to a depth of several thousand feet. The weight of the ice alone caused the continent to sink. As the glacier receded, the land recoiled and lifted to almost its present level above the ocean. Probably the biggest event in terms of visible effects that were left for us to see, the glacier gouged out less resistant rock, moved huge amounts of crushed granite, and dug out deep hollows in the mountains that had formed earlier.

One famous specimen of glacial activity that is also visible in Acadia National Park is Bubble Rock. It’s a giant boulder picked up by the sheet of ice and placed on the edge of a cliff on South Bubble Mountain. It’s called a glacial erratic because it’s rock of a different type than the bedrock on which it sits. It could have come from miles away.

The ice also carved a giant gash almost through the middle of the island. It is Somes Sound, the only true fiord on the Atlantic Coast, because it was formed by the glacier and not erosion. There are great views of the sound from the tops of Acadia Mountain, Flying Mountain and St. Sauveur Mountain located on the western side of the island. Eagle Lake, which is visible from Cadillac Mountain’s North Ridge Trail, was also carved out of less resistant rock than the granite mountains.

But the greatest place to hike and witness the effects of a moving, massive sheet of ice on rock is Mount Katahdin. The ice, carrying rocks imbedded in it, acted like a coarse sand paper and shaped the mountain we climb now. As the ice froze and melted it moved vast quantities of rock up one side of the mountain and down the other. The mountain itself is made of a molten, granite magma chamber that formed all those millions of years ago under the sea, then solidified. It was no match for the weight of all that ice and rock, though, especially on its north and east sides. There, the retreating continental glacier left mountain glaciers that created huge cirques or basins. The exposed granite magma is visible in the vertical cliffs of the Great Basin at Chimney Pond.

As you hike to the top of your favorite mountain or take a path along a lake or seashore, look down at the rocks under your boots. That ledge you just crossed could have started as molten rock under the ocean. The view from the top of your favorite hill might have been created by glacial action. You’re witnessing the effects of an enormous passage of time on the landscape. It sort of makes stopping to look at the view or even the rock on which you rest a little more meaningful to the present.

Additional reading on Maine’s geology:

“The Roadside Geology of Maine,” by D. W. Caldwell is a good sourcebook for understanding more about how Maine was formed. It has some good trail information, particularly on Katahdin, as well as what you can see from the car throughout the major roads of Maine.

“Underfoot: A Geologic Guide to the Appalachian Trail,” by V. Collins Chew describes all the mountain building events that created the Appalachian Mountains, including Maine. The Maine section describes the trail underfoot through all of Maine’s 278 miles of the Appalachian Trail.

Brad Viles of Ellsworth is an avid hiker.