The Rock Hard Marathon lived up to its gritty name during its three-year run from 2014-2016 at the Freetown-Fall River State Forest in Assonet, Mass., challenging runners with plenty of singletrack and rocks with some tough hills thrown in for good measure.

The event is growing into an ultramarathon in 2017 and adopting a new name: the Freetown 50K.

“Originally we were ending the event, but so many runners expressed interest in a 50K distance that we wanted to give it to them,” race director Michael O’Connell said in an email.

The race will take place at 9:30 a.m. Sunday, Sept. 17. Registration is $55 and can be done via UltraSignup.com.

O’Connell said that in the interest of keeping the race small, he initially instituted an application process for entry, but has since opened it up to everyone. Runners should be prepared for some tough running. The course measures closer to 35 miles, so it’s a “heavy” 50K with a nine-hour time limit. There’s no pavement; it’s all technical singletrack or fire roads, and runners will twice ascend the course’s two biggest climbs – Hold On Loosely and the Fire Tower.

“Hold On Loosely is a steep grade fire road with loose gravel that slides around,” O’Connell said. “The Fire Tower is this amazing technical singletrack climb that takes you to the overwatch tower that overlooks the entire park. The descent from that is pretty wild.”

O’Connell noted that the Middlesex Fells and Blue Hills Reservation trails are good comparisons for the type of terrain runners should expect at Freetown.

“This wouldn’t be a beginner’s first ultra,” O’Connell said. “Racers who know how to manage their nutrition and pace themselves well are going to love it, especially those who like technical trails.”

Jason Paganelli vouches for the difficulty of the Freetown trails. The race director for the Anchor Down Ultra in Rhode Island, Paganelli raced the Rock Hard Marathon each of the past three years, and he’ll toe the starting line for the 50K this year, too.

“This course is awesome, and grueling in a unique way,” Paganelli said. “Without much elevation gain aside from a few challenging climbs, the rocky nature of Freetown makes for a super runnable course from an elevation standpoint, but a super ‘grinding’ course from a footwork perspective. You find yourself really racing and running the smooth sections, and then taking on the rockier sections slower and slower as your body starts to reel from the course. It’s hard in a unique way for the area, and I think it’s what makes it special. It beats you to a pulp mile by mile … it’s awesome.”

As has been the case in previous years, the run will coincide with the Freetown 50 Mountain Bike Race. Runners and cyclists will share the trail, which O’Connell said brings extra energy and camaraderie to both events.

“We find that mixing the two events works well, just like it does at the Vermont 50,” he said. “We get two user groups looking out for each other and cheering each other on. We actually changed the whole course to better work the mix and achieve the distance that we were looking for. Our mountain bikers are pretty psyched about it, too.”

While O’Connell is excited to give runners an opportunity to log ultra mileage this year, he also is eager to showcase the Freetown trails to runners who’ve been there before and also introduce new runners to the state forest.

“DCR Freetown-Fall River State Forest is such a unique place and sometimes you turn a corner and are in what seems like a totally different park,” he said. “The place is huge and has something for everyone. We like it because it’s unapologetically hard, the way it should be.”