Voices in Newton County, Arkansas

My son's father and I came over from Oklahoma to the Buffalo National River area. I picked a waterfall out of my waterfall guide book that we were going to go find. We chose Hideout Hollow. When we pulled up to the parking area at the trailhead he turned off the car. Our windows were down because we were both smoking a cigarette. At that time I heard what sounded like if you were in the bathroom and heard your dog sniffing under the door. I asked him in a whisper “Did you hear that?” He said “That sounded like heavy machinery off in the distance.” I let it go because I was just grateful he acknowledged the sound. We started to head down the trail when I realized we left our hiking sticks in the car, so I ran to get them myself. I had a slightly creeped out feeling but didn’t worry about it too much because I could still see him the whole time. Once I got back to him we started down the trail. We were just starting to round the corner that goes to the left when we heard a rustling in the trees to our left. We both stopped started and looked. We saw a huge figure running through the trees. I thought it was a man at first until I realized it was totally covered in hair, medium chocolate brown in color. I remember seeing it’s arms in front of it as if it was moving branches away to protect its face and its hands were black. I whispered “what was that?” He whispered back “I have no idea” I whispered “do you wanna go back?” And he nodded his head yes quickly. The direction it was going, it would’ve crossed the trail just around the curve. We turned around and started walking quickly back towards the car, both of us constantly looking over our shoulder behind us. I started asking questions to make sure we saw the same thing and neither of us forgot. We agreed it was on its hind legs, it was brown, it was a lot bigger than us and it was fast. Suddenly something flew fast over our heads (a rock?) hitting leaves and branches. I turned at looked at my son's dad with a “what the heck?” look on my face and his eyes were huge. We ran the rest of the way to the car. I had never been so scared and I wasn’t sure we would make it back to the car. We did and immediately he began second guessing what we had just seen, suggesting maybe it was a bear, a deer, an elk, etc. I asked him if he’s ever seen a bear run like that on it’s hind legs, or a deer or elk that dark running that smooth, he said no. We went to the Tea Kettle falls area but I was too scared and anxious to get out of the car again, convinced whatever it was could have easily covered ground by then. A Google search once we had service said only black bears live in Arkansas and I’m positive what we saw was brown. I didn’t notice any smells but since we were talking I also didn’t notice if it was quiet or if any birds or bugs were chirping. I know I have no desire to return to the area, I get sick to my stomach any time I think about it.