A carpenter and myself were installing wooden flooring in my house out on the prairie in the foothills of northern Colorado, 2 miles west of Rawhide Energy plant, 2 miles east of the Front Mountain Range. It was near midday and very clear blue skies, no wind, cool about 70 degrees F. It is a very rural area with ranches all around but miles between them.We both stepped outside for a break and what caused us to look skyward was the enormous number of contrails at high altitude crossing the mountains. We had never seen that many commercial aircraft going both east and west. As we looked up directly overhead, we both saw a small hovering object, right above us perhaps by a few hundred feet or more, hanging motionless. It was easily seen, in broad daylight. It was a device unknown to me, as I am an ex military and ex flight school candidate and familiar with aircraft and helicopters.It was a faceted shape, very much like an old lunar lander in appearance, but with no landing legs or protrusions. On the underside, which I assume we were staring up at, were two large globes. My carpenter asked "What is that?" and as we both stared at it, I said I really don't know. This thing hung over us for some seconds, then a faint glow rose up in the two globes and it slowly began to move. We watched it slowly accelerate to a moderate speed and gain a little altitude as it flew north / northeast toward Wyoming only 20 miles away. Once it was no longer overhead I could clearly see the angular faceted shape of the body and the two globes on the underside. I estimate 1000-1200 ft altitude initially in hover, gaining up to 2000-2500 upon exiting the area north. We watched it until it was out of visual range.It made no noise at all. The overall color of the device was a very subdued dark green-grey, very much like a military aircraft color. We speculated among ourselves at the time that this could be a military surveillance probe in testing, but if so it uses a technology for flight that is not yet public knowledge, as it had no wings, no rotors, no visible means of support other than twin glowing globes on its' underside. And it was silent, transitioned smoothly from hover to level flight, accelerated very gradually, and displayed no erratic or sudden radical maneuvering. It was however NOT a conventional air vehicle.Withing a few days, we found a dead antelope about 50-60 yds from the southeast corner of the house. Antelope are very common in large herds in this area. This however was odd as it appeared to be a fairly young healthy animal and was not attacked by predators. It was lying on its' side, quite dead, with a large round hole in it's left hindquarter, bigger than any firearm other than a 40mm grenade launcher could make. No scorching, no blood, and no exit wound. Just this big perfectly round hole. Within two days, coyotes reduced the carcass to clean bones and we found no trace of metallic projectiles or shot. We have no idea what killed this animal.We do not know if there is a connection between the two events, but it is curious how close together they occurred.