"It was on the north side of the Canyon," began the topographer, "and I was working on an outlying butte with my assistant. We had made quite a number of bench marks and I was working out the contours--those are the lines on a map which show the height or elevation of any point--while my assistant was sitting beside me, making out some of the necessary calculations. We were working out from a little side camp, the two of us, the rest of the party being at headquarters, several miles away. I was drawing in at full speed, because I wanted to change from that side station that evening, and for a couple of hours I suppose we had not exchanged a word, except with relation to figures. "Before coming out on that sun-baked exposed butte, I had tied the animals--a pack-mule, my riding mare, and the assistant's horse--to the branch of a tree. Suddenly, as it afterwards appeared, the other fellow heard a sound as of a fall and went to see what it was. He was gone so long that I noticed his absence. When he returned I waited for him to volunteer an explanation but apparently he did not want to disturb me, so I said, questioningly: "'Well?'" "'Only two of them there now,'" he replied. 'Bella's gone over the edge. Neck's broken, so there's no use doing anything.' "Now Uncle Sam, you know, is always willing to stand for accidents that can't be helped, but he's got to know all about it, and while I realized that it would really matter little in the long run, I was sure that the department would feel better satisfied if the manner of the accident were set forth. So I put away my pencil, folded up the plane table, and went to investigate. It was as puzzling a thing to decide as I ever saw. The tree was at least twenty yards from the brink of the precipice, although the ground sloped fairly steeply to the edge. "When I arrived there I found the other two animals tied to the branch, as I had left them, and apparently undisturbed. The ground, however, between the tree and the edge of the chasm, was torn up with hoof marks and the struggles of an animal that evidently had fallen to the ground, and the spoor from the tree to the Canyon's edge was easily traced. Of the animal, I could at first find no evidence, but my assistant touched me on the arm. "'Here, Mr. Masseth,' he said, 'you can see Bella from here.' "Sure enough, on rounding the corner of a pinnacle which stood out a little distance from the edge, the body of the mare could be seen about one hundred and seventy-five feet down, lying on a sharply pitching bank of talus--that is, debris of rock and dust, fallen from the overhanging cliff above. It was still a wonder to me how the mare fell, and as she had been wearing a brand-new halter, this in a country where it is easier to get beast than harness, I told my assistant that I was going down to secure the halter and also to find out, if I could, what had been the cause of the accident.