Shortly after the arrival of the visitors, we were terribly alarmed at a sudden prairie conflagration. The old grass of the valley in which we were encamped had not been burned off, and one of our cooks having unwittingly kindled a fire in the midst of it, it spread at once with wonderful rapidity; and a brisk wind springing up at the time, the flames were carried over the valley, in spite of every effort we could make to check them. Fortunately for us, the fire had broken out to the leeward of our wagons, and therefore occasioned us no damage; but the accident itself was a forcible illustration of the danger that might be incurred by pitching a camp in the midst of dry grass, and the advantages {30} that might be taken by hostile savages in such a locality. After the fire had raged with great violence for a few hours, a cloud suddenly obscured the horizon, which was almost immediately followed by a refreshing shower of rain: a phenomenon often witnessed upon the Prairies after an extensive conflagration; and affording a practical exemplification of Professor Espy's celebrated theory of artificial showers.[83] [Pg117] We now continued our journey without further trouble, except that of being still forced out of our proper latitude by the northern bearing of the Canadian. On the 30th of May, however, we succeeded in 'doubling' the spur of the Great North Bend.[84] Upon ascending the dividing ridge again, which at this point was entirely destitute of timber, a 'prairie expanse' once more greeted our view. This and the following day, our route lay through a region that abounded in gypsum, from the finest quality down to ordinary plaster. On the night of the 31st we encamped on a tributary of the North Fork, which we called Gypsum creek, in consequence of its being surrounded with vast quantities of that substance.[85] Being compelled to keep a reckoning of our latitude, by which our travel was partly governed, and the sun being now too high at noon for the use of the artificial horizon, we had to be guided entirely by observations of the meridian altitude of the moon, planets, or {31} fixed stars. At Gypsum creek our latitude was 36° 10′--being the utmost northing we had made. As we were now about thirty miles north of the parallel of Santa Fé, we had to steer, henceforth, a few degrees south of west in order to bring up on our direct course.