Spider identification help

I was on vacation out in South Dakota in August and came across this spider one night. I am seeking assistance to identifiy what type of spider this may be. It was about 4 1/2"-5" wide including the leg span. It was dark brown to almost black in color, and moved very quickly. Is it poisionous?

Can you send a photo of your spider? It's very hard to ID them without one as so many look similar
glen