Guy, great job and thanks for catching us the correct family. I'm not that familiar with them yet and I live way out in the desert.
After looking at those two suggestions of yours, I'm leaning towards an adult female D. vitattus, since the legs are not that brightly striped, but I'm still not sure if that is a discerning quality, between the females or not.

Thanks guys! I did look at Dolomedes tenebrosus for this spider, just because of the sheer size of it. D. tenebrosus is the largest spider we have in Maryland, and this was definitely near water. The markings or lack thereof are confusing me, though. I haven't found any photos of that species with such faint markings. That's why I was also still looking at Hogna, because the shape seems to fit better--hogna carolinensis is a close second for biggest spider here. But still not sure about the markings.

Looking at D. Vitattus, yes, that is the closest thing I've seen.

Another note, I went back to see if I could find her again the next day. This time, she was on the ground, and saw me before I saw her. She ran very fast toward the edge of the stream, which was actually a steep drop off, not a bank she could run down. I couldn't see if she rappelled off the edge or just went under some overhanging vegetation.

Well, good to know it's a she! I was thinking hogna, but it looks like the discussion continues ;-)