Avery Mornis leads Eric Ellingwood over ledge rock that will likely remain part of the mountain-bike trail they are building.

ORLAND, Maine — A half-dozen volunteers were hacking about 4 miles worth of mountain-biking trail into the side of Great Pond Mountain on Wednesday. It was grinding work.

Small black flies hovered a dozen at a time around the diggers as they shaped the trail with shovels and hoes. The ground was soaked, thick with rocks and roots, and dotted with orange flags that the workers used as guides.

The volunteers have an ambitious goal. As members of the Penobscot region chapter of New England Mountain Bike Association, they want to build the first extensive mountain-biking trail system in Hancock County. Doing so would make the county a destination for bikers around New England, said Craig MacDonald, the chapter’s president.

The particular trail being built this summer will slalom horizontally down the 1,020-foot mountain, MacDonald said. He hopes the volunteers will finish it in mid-November. This construction follows a 530-yard, single-track trail that the chapter helped build in the same area, on 4,500 acres owned by the Great Pond Mountain Conservation Trust off Route 1.

“It’s being done in bits and pieces, here and there,” MacDonald said Thursday. “I’d say we have three-quarters of a mile pretty close to complete. We have accomplished a lot in a short period of time, considering that we started construction [a] little less than a month ago.”

To one trail builder, 25-year-old Avery Mornis, the work will finish a dream that began about five years ago. A resident of South Reading, Vermont, Mornis helped design the trail as a University of Maine student before graduating with a civil engineering degree in 2016. He has manned a mini-excavator on the mountain for the last three weeks “to build what I have envisioned.”

“I have had this in the back of my mind since I graduated,” Mornis said. “There is not a whole lot of riding in Maine that exemplifies this style, with big berms, high speed sections and jumps and natural sections as well. Great Pond Mountain has this really unique terrain and I think this takes advantage of that really well.”

The trail will skirt car-sized boulders and run through thick stands of Hemlock and beech and over large sections of exposed ledge, said Mornis, an avid rider who has biked trails in Old Town, Camden, Falmouth and the Carrabassett Valley.

“The biggest benefit of this is it adds a lot of character to the trail. A machine-built trail can often feel a bit boring because it doesn’t have that mix of natural features,” he said.

Though the mountain is steep, the trail’s horizontal meanderings will leave riders on what will feel like a gentle slope, MacDonald said.

Finding the right way through the boulders and trees is a challenge.

“Pretty frequently you run into issues. Sometimes you can’t find enough dirt and material to build what you are envisioning where you initially envisioned it, so you need to make a reroute or a change to the layout to be able to accomplish what you need to,” Mornis said.

The trail will be built to last, MacDonald said.

“We use the contours of the landscape to limit erosion,” he said. “There is a lot of thought about, what is the water going to do to this trail? Sometimes you’ll have something there that looks like a jump, but it’s not. It’s a rolling grade-reversal to control water, but it’s also fun to ride over.”

MacDonald invites interested parties to visit prnemba.org to make donations or volunteer to work on the trail. Without volunteers, the trail would likely cost about $45,000 per mile, he said.