Thanks to Josh for the attached great map and route which i have altered a bit from when he led this a few years ago. It can be somewhat confusing so anyone who likes can stick together. There are several shortcut options. There are some ephemerals and nice spring views.
Note that you can no longer park outside of the Park, you have to drive in through the gates and park in one of the lots. They don't open the gates often until a few minutes after 8 so if you are running early stop somewhere along the way at least 20 minutes before you get there - there's no longer anywhere to wait there or close by until they open the gates.
To get to the parking area, head for I-270. From Exit 22, take Rte. 109 South towards Barnesville. In about 2.5 miles come to a 4-way stop. Turn right onto Comus Road and go for about 3 miles to a T-intersection with Mt. Ephraim Road. Turn right and go for about three miles to a five-way road junction. The entrance gate is at the second right. Go along the entrance road past the East View parking area, continue to the large West View parking area past the west view sign, roundabout and pavilion (portapotties). This road has several switchbacks.
About an hour's drive from Carderock.