Visually observed Delta shape over the foothills adjacent to Stillhouse Lake, Texas - just south of Killeen / Harker Heights

Around 10 P.M., we drove to a small lakeside park - by Stillhouse Hollow Lake, in the foothills- just adjacent to the 3481 Stillhouse Lake Bridge.
After approximately an hour, we decided to call it a night - and head back to my place.
On the drive south - I looked out of the passenger window (facing west) and commented that a nearby 'cloud' was oddly delta-shaped. After a few minutes, we decided to pull over to the shoulder of the road and take a better look. At 11 p.m., the driver, Ryan Keaton, jumped out of the truck to snap a few pictures with his cellphone.
We could not believe what was photographed. Afterward, we continued to drive back home, I looked in the rearview mirror - and at first, thought the hills were on fire. After closer inspection, I realized that the 'fire' was up in the sky above the mountains, and in the shape of a giant triangle. It was quickly descending. Ryan then saw it too. We then turned the truck around - hoping to find a good place to snap more images. Unfortunately, the thing fell below the hills - and we didn't see it again. But luckily - we did have the first sighting images. They are posted in chronological order. They are not as dramatic as what we saw afterward, but please have a look and them. It has now been more than an hour since the event, and my heart is still pounding. This object was higher up than it appears and was monstrous in size.