The feeling of being watched in Tom Green County, Texas

It has been a very long time but I just can't seem to forget that day. Let me start by saying that I knew the area fairly well - I used the riding trails as relaxation for my horse. I would ride in the area at least once a week for a couple of years. I knew the different trails and the animals and birds that usually occupied the area. I had been riding for approximately 30 minutes when we came upon a ridge - my horse began to walk very cautiously almost as if he was getting nervous. He didn't make a sound but you could tell he felt uncomfortable. His ears were pointing towards the front and he was watching the ridge very closely. I noticed that it was completely silent which was strange for the area. Usually the mockingbirds and scissortails would follow you from tree to tree but not this day in this area. We came up to the top of the ridge and began walking down a narrow trail when my horse began to shake. I remember like it was yesterday that I began to feel like I was being watched and became a little scared myself. Then my horse jumped to the right, I looked over to the left expecting to see a rattlesnake and squatting in a large brush (a group of bushes - not just one bush) was something large - it was very dark and scared me to death! My horse took off running. I couldn't hold him back at all - he was scared, very scared. I remember looking back and seeing something come out of the brush but I never could tell height or weight because of the winding trail. You could definitely make out that it was covered with hair, I say that because I didn't see any clothing and it was covered - no skin was showing. We came upon an area with a small clearing and I forced my horse to stop - I looked back to see if anything was following us and I saw nothing. Regardless my horse wanted out of there and began pawing at the ground. He wanted out of the area. We made it back to the horse trailer in just a minute or two. My parents were there and saw the fear in my face and how scared my horse was. I told them what happened and they never questioned me - I was pale white and the horse was ready to leave - he never acted like that. I think they thought it was a person hiding out and didn't ask anything else. I would never go back to ride in the area again. I don't know if it was a transient or what but I can't imagine someone just hanging out there. Especially in the brush - I am not sure what kind of brush it was but it was the kind that would cut you to pieces. The area was mainly motorcycle/horse trails but very few people used them. The area was not far from the lake and there was ranchland to the north. The day was hot with a gusty breeze - I remember that because I was wearing a t-shirt and shorts. I know it was fall because I was back in school. I know the ecology doesn't seem to fit the habitat of a bigfoot but I just can't figure out what it was. It wasn't a black bear or big cat because it was coming out of the brush in a upright position not on all fours. You could tell it was going to stand up - thankfully my horse was scared enough I never had to see the actual height. There were some berries in the area and plenty of rodents so that might be able to sustain a large animal for a short time - perhaps he/she was just moving through the area. The area is now a state park and the particular place I had the encounter is no longer accessible, and even if it was, I would not go back to even try to find the spot. It is not a remote location anymore due to urban sprawl. At the time there were very few homes in the area to the north - it was primarily cattle and sheep ranches.