It was some time before I dropped off, as there were several problems connected with the trip that I kept reviewing in my mind. I could hear Olin’s steady breathing, and envied him his ability to sleep soundly under any conditions. Up from the east swam a large, perfect full moon, flooding our camp in the little arroyo with its cold light. From far away came the indistinct, silly yapping of a couple of coyotes, and I could hear the horses stirring uneasily. Finally I fell asleep, and it seemed as though I had hardly closed my eyes when something--perhaps a sound, or maybe a premonition of something wrong--caused me to become wide awake. I sat up and, noticing that the moon was now overhead, looked at my wrist watch. It was almost one o’clock. There seemed to be nothing amiss. Olin was snoring peacefully, the coyotes were no longer serenading the moon, only a little breeze was moving the tops of the mesquite brushes. I glanced over to where the horses had been tethered, and saw that they were very restive. Thinking that perhaps some coyote was skulking about our camp, I crawled out of my sleeping bag, took my rifle, and went over to where the horses were trembling and straining at their tethers. They were apparently scared at something immediately in front of them, as they both gazed with bulging eyes in the same direction. Aside from a large rock and a few straggling sotol plants, I could see nothing to cause their fear. Thinking that perhaps, some creature had hidden behind the rock, I made my way in a wide circle around it, but there was nothing I could see to explain the horses’ fright. I went to them and stroked their noses; this calmed them somewhat, but they continued to gaze fearfully at the rock. IT came over me like a flash that I had not noticed that rock when we made camp--in fact, being now fully wide awake, I recalled that there was no large rock of any kind near our camp. I blinked my eyes and pinched myself to see if I was really awake. Could I have been mistaken about my first impression of our camp site, and have overlooked an object as large as that rock? My work has always called for keen observation, and it was absurd to think that if a fairly sizable boulder had been in sight, especially all by itself as this one was, I would have failed to note it. Yet there it was, gleaming dully in the moonlight, apparently firmly imbedded in the ground. But it _couldn’t_ (I reasoned) have been there when we first arrived. Imagine two geologists failing to see a rock of that size! How in the world could it have gotten there? Was it placed there by someone during the night, while we slept? And if so, why? But I had not noticed any footprints around it. It was obvious that it could not have rolled from anywhere. It had not been there four hours ago, it had not been carried, it had not rolled . . .