From the spot you are parking at BBD, you can reach it from either direction. You can follow the main trail as the numbers decrease until you eventually get to the shell covered road over by the river. Take the Shell road until you can either go right on the main trail or straight on to Hearbrak Ridge. I believe that is the #18 sign post. You will also see a yellow sign for Hearbreak Ridge. If you follow Heartbreak Ridge you will dump into Washboard. At the end of Washboard you will be at the power lines. You have several options at that junction. You can go left and go down to Indian. Right will take you to Grandpa, or "the pig trials" as I call them (techno pig, piglet, hogwild, you get the point) or you could go on to the main trail. any of those will eventually get you back to the main trail. Once you get across the street you can either take the levee back, or there is some single track that follows part way (47-41 in descending order).
If you follow this general route from BBD you will spin in the neighborhood of 18-19 miles.
Or.....You could park in the parking that is on the south side of the street on Morris Bridge Road. And hop into the trails at trail #5 ( this is called the hole in the fence) . From there you only have a mile or so before you reach some of the more (slightly) challenging trails.
Hope that helps, Gregg