If you are a purist, you will want to start at the official beginning, at the ruins of Seneca Mill, or at Riley's Lock, where Seneca Creek flows in to the Potomac river. In either case, the first mile is walking along a road. Since I'm not a purist, and I don't enjoy walking along the side of roads, I started just across River Road, on Seneca Rd. There is a wide shoulder there with enough parking for 3-4 cars.
This trail goes through varied terrain, sometimes heavily wooded, sometimes meadows, and everything in between.
If you aren't familiar with the Seneca Creek Greenway trail, it runs all the way from the Potomac River to Watkins Mill Road, a total of 24 miles. North of Watkins Mill, it continues as the Lower Magruder Trail.
The first 1.3 miles connects Seneca Road to Berryville Road. It is a hilly section of the trail with lots of ups and downs. The trail is forested and shady. There are a couple of small streams with wooden bridges over them.
Along the way I saw this old log with a mass of miniature mushrooms growing out of it. I was surprised both at how many there were and how small they are. Other parts of the trail in this area have ferns growing right up to the trail's edge.
Towards the end, it can get confusing, what looks like a path that leads off to the left with access to the creek is really the main trail. Go down the hill and cross the creek on stones. If you get to a road (Berryville Rd), you've gone too far, but don't panic, just take a left and walk along the road until you see a parking area and the trail again.
At the parking area, the trail continues on, 4.4 miles to MD Route 28. This post won't cover the whole way, just to the Berryville Road Side Trail.
Seneca Creek is deep and wide here. Lots of families come to splash in the water and swim. Shortly after this area the trail veers away from the creek and you won't see much of it again, so enjoy the water now. From here on the trail is mostly flat with the occasional hill.
The trail has mile posts every half mile so you can keep track of your progress, it also has these blue posts with the trail name on it. Even with that, it isn't all that well marked. There are lots of side trails and it sometimes isn't clear which trail is the main trail. It would be nice if they had signs where trails met so you know which way to go.
There are a couple of places where you can see signs of the past. Here is a couple of long refrigerator cases. I'm not sure how they got here, and they have obviously been here for a while, but out in the middle of the woods, just a little way off the main trail is this old refrigerator case from a grocery store.
A stretch of the trail goes through a meadow. Here is near the start, as the trees give way to grass.
Another sign of the past. In some places you can see remnants of fence from before this area was a park. Here, right by the path, are several strands of barbed wire coming out of a tree.
The trail crosses a number of small streams, many of them have bridges built over them.
One of the few marked side trails is this one, the sign says Berryville Road side trail, and it should take you back to Berryville Rd. This is where I turned around. If you want to see what there is if you continued, read my post on the trail starting at MD-28. You can also learn more about Seneca Creek on Wikipedia.