Whooping in Douglas County, Oregon

My brother and I went camping in the area between Glide and Diamond Lake on Highway 138. We pulled into a forest Service campground named Eagle Rock and found we were the only ones in the campground. The campground is situated right alongside what I believe is the Umpqua River. There are steep mountains on both sides so I guess you would say we were at the bottom of a canyon. The water was running over a lot of rocks next to our site and made a lot of noise. My brother decided to pitch his tent next to the river and I slept in my van in the parking spot. As darkness fell, we sat out in the dark talking about our lives. This was the first time we had been together in about 20 years so we had a lot of stories to tell. While we were was talking,I heard something making a weird calling noise from the mountain across the river from us. I wasn't sure until I heard it a second time. Since my brother was talking at the time, he didn't hear it. We eventually headed off to our respective beds. My brother woke up at 0200. He said he was checking his watch fo the time when he heard 2 loud hoots from across the river about 50-100 yards downstream. He called them hoots but said it wasn't really a hoot. He couldn't really describe or imitate the sound. They had to be very loud to be heard over the noise of the river. He laid frozen in his sleeping bag then heard something walking around the campsite. About that time something woke me up. I heard something moving around outside the van and was about to raise the windowshade to peek out when I heard what sounded like a gorilla grunting next to my van. I have no real experience with gorillas and have only heard them on nature shows on TV, but that's what I heard. Needless to say I was too afraid to lift the shade at that point. After a while, it got quiet (except for the river noise) and somehow we both fell back asleep. When it finally got light we came out, compared notes and started looking for any tracks. The ground was too hard and the river too rocky to show us any. I also checked the campground to see if there were any other campers there, but there were none. We don't think it could have been deer or elk because it was right in the middle of hunting season and hunters are all over the place up there. I don't think any deer or elk would come into a human camp at that time of year. When we got home we listened to the recordings on the site. The calls I heard were similar to those on the site, and my brother thought what he heard sounded similar.