With the weather being so hot lately I have been trying to get rides in before work to beat the heat. I did some Oak Hill climbing yesterday afternoon and my legs were feeling it today so I decided to swing over to Mast Yard in West Concord since it is close to work and more importantly - flat. I have ridden here before but it consists mostly of deer fly infested fireroads and only one singletrack trail to my knowledge (~1 mile), but I heard that they put in a new snowmobile bridge this year and wanted to see what was on the other side.
I'm glad I did, because there is a bunch of fun, really fast, buff singletrack once you get over the bridge. There are a bunch of nice sandy beach areas for taking a dip when things are too hot and there were a bunch of side trails that I didn't take so I suspect there is more. It certainly warrants another trip when I have more time to explore. All told, I did just over 10 miles with a 50/50 mix of singletrack to fireroad. If you are looking for a non-technical really fast trail system for some tempo training rides or if your a beginner then this would be a great place to go.