Route: Mt Greylock, Thunderbolt Trail (MA)

Massachusetts, US
13 mi

NOTE:  The Department of Conservation has asked hikers to stay off the Thunderbolt Trail in summer to prevent erosion!


Patrick Begley:

The Thunderbolt Trail is between 2 and 2.5 miles long with an elevation gain of 2,275 feet. A typical hiking time of the trail is between 1-2 hours. It is the shortest route on Mt. Greylock and therefore has the steepest gradient on the mountain, reaching angles of 35 degrees. The trail is rocky and thin at the steeper sections, and rocky but wide on the lower sections. It begins with a short section of switchbacks before making a nearly direct climb of Greylock.

I, Patrick Begley, had just gotten off a high school cross country season and was in relatively good shape despite taking a week off. I planned to finish my season with an FKT of the Thunderbolt trail and noticed that no times had been reported. I left for Greylock on November 10th at 8:30 a.m. from CT and arrived at around 10:15 a.m., following a recent snowstorm that had since melted. I began my run with a large group of friends down at a different trailhead to have a flat warmup before reaching the Thunderbolt Trailhead. At the Thunderbolt trailhead, I left my friends and started my watch. At the steep gradients, I had to walk in some sections but perservered. For the entire run, I was running in a shirt, shorts, hat, and running shoes through a snow cover on the trail from the storm. At the top, the temperatures dropped in the wind and the snow was around 3 inches deep. I reached the summit tower in 34:21 and finished my ascent there for a self-supported run FKT. I then returned to another runner in my party, about 3/4 of a mile behind me, and I ran with him to the summit. I then ran back to the majority of my party, about a mile below the summit, and ran with them to the top once again, reaching the summit three times. By this point I couldn't feel my fingers and could hardly feel my legs. I then descended the Long Trail with the group and without a timer, running the majority of the way. I had lunch at a local deli and returned to CT.


Drew Best added detail:

I ran the Thunderbolt Trail today in 29:24.  Because this may be a new FKT and there are very few recorded/verified attempts with precise route details, I thought it important to firmly establish the route today.  I heard from a few local experts, checked a few maps, and most importantly, checked out the trail during my warmup and found a bunch of signage clearly indicating where the trail goes.  

Thunderbolt Trail route details:

--The trail starts a little ways (a few 10ths of a mile?) past where Theils Rd in Adams, MA, is blocked.  The remaining paved road (after the road closure) turns to dirt and meets up with a new, crushed-gravel loop that circumnavigates a pond at Greylock Glen. A few hundred meters after Theils Rd turns to dirt, there is an obvious trail junction dead ahead.  Perhaps 20 feet up this trail junction, there are signs on 2 trees indicating the start of the Thunderbolt Trail.  I considered the very beginning of this trail-- about 20 feet back, where it meets the dirt road-- as the beginning of Thunderbolt, and I began timing my split here.

--After perhaps 1/4 mile, the trail bears right.  There is old signage on a tree. It's worth noting that the bottom half of the TBolt is blazed blue (very old paint).

--After perhaps 1/2 mile, the trail makes a quick left turn onto the Roost Trail. This turn is not marked, but after running down this left trail for 100M at the most, there is signage indicating that the TBolt continues to the right.  You'll miss this whole section and end up off-trail if you're not looking for the forementioned left turn. 

--Now the trail is obvious for the remainder of the ascent, which gets very, very steep.  The middle portion, beginning here, seems to follow (finally) the old ski slope. Brutal. 

--The TBolt joints the Appalachain Trail.  Take a left and run for perhaps 1/2 mile up the AT.  This section is less steep.  Cross the auto road. Continue on a very short stretch of pavement/gravel to the Summit Monument/Tower, and tag it to end the segment!

-My Suunto Ambit3 Run recorded this route as 2.10 miles.

Details from my effort today:

My friends Matt Shamey and Aaron Stone hiked up via a similar route.  We started at 9:15 AM from Gould Rd/Greylock Glen.  I warmed up on lower trails and the first mile of the TBolt, getting lost but finding the trail, and running down this 1st mile to be sure I had the right route.  I ran the trail using the route described above in 29:24, tagging the monument to finish.  We spent about 30 min at the summit and then ran a nice ~8 mile route along the AT and Old Adams Rd to get back down the mountain.  My mark can be improved upon, no doubt.  I train for mountain races and am in competitive shape right now, but I was hampered by a very sore L calf and achilles, and I know of at least a few guys who could challenge this mark.  I'll come back later this year or next spring at the latest in an effort to lower this time. 

Previous FKT attempts:
In addition to the first post in this thread, I'm aware of other attempts that warrant mention.  The Greylock Trail Race begins by climbing to the summit via a similar route, but one that does not use all of the Thunderbolt.  Several if not many fast ascents have been recorded using this route, which might be a great FKT in its own right, but this is not the historic or even current Thunderbolt.  Also, Ted Sloper offered this information: "Back in the 1960's The Mt. Greylock Ski Club ski team (coached by John Howe) would train in the fall before any snow. We would run UP the Thunderbolt and if I'm not mistaken Colin Garstang held the record @ 24 minutes. We would start at Thiel farm and end by touching the monument."  In light of potential ambiguity regarding these performances and the routes taken, and changes to the trail that have occured over the years according to some sources, I propose my effort today as the "modern FKT" for Mt. Greylock.  Admins/others, feel free to disagree!

My run:

A good reference:

-Drew Best, Amherst MA


Neil Clauson notes that the Strava segment for this (listed as Notch Road Climb) doesn't start at the very bottom or end at the very top.  Drew's time for the Strava segment is 25m47s, vs. 29m24s for the full Thunderbolt Trail.

GPS Track


I have been on Thunderbolt several times this year (spring, summer 2021) and have never seen any evidence to stay off the trail.