It's a pretty small area, no more than a few acres really. You will get some nicer rides if you take the old Howarth-Hebden road then at Peckett Well drop down a really challenging bridleway by the garages to the NT car park at the bridge (forget the name). Also from the modern Hebden-Howarth road there's a smashing BW that goes up over the tops and drops down into Luddenden Dean, it's one of the best downhills in the area. On the Howarth side you can contour around the hillside by using the old Victorian drain systems.
You really need to go and buy the OS 1:25,000 scale map of the South Pennines, it's absolutley loaded with fantastic MTB trails - look for the dashed green lines, which are bridleways. It will be the best little investment you've ever made.