Park in the Putnam Park Parking Lot to start (very near the trail end, 1 mile from the Putnam County Veteran Memorial Park main building on the right), then continue by bike north on Gypsy Trail Rd.
Take your first left up Mt Ninham Rd, climb the steepish pavement for 5-10 minutes. At the gate, and small parking area (you can shuttle if you really want to) find the trail entrance on your left across a small stream. After about 100 feet, turn left up slick rock embankment (not always obvious) to a small clearing. The singletrack begins here, though foliage and leaves can make it a bit unclear at the beginning, it soon becomes well established.
There are a few options now, but all roads lead you back to Gypsy Trail Rd within a few hundred feet of the parking area. There are a few large, totally optional hits, and some medium features, drops, logs, stream-crossings, and otherwise it's rocky, fun, twisty riding. It is just a warmup for the rest of Putnam Park, but super fun for a quickie.
You can also continue climbing past the gate, the pavement turns to dirt and you can double or triple the ride by adding the upper Ninham.
And then check out the rest of Putnam Park.