All dams were begun at the surface and no sticks or stakes were driven down in beginning to hold in place the sticks that were to compose the bulk of the structure. Earth and stones, the latter of as much as six pounds each in weight, were brought to the spot and piled on the sticks. Trappers asserted that they would load each other's backs with earth and stones to be carried to the site, but this statement is not sufficiently authenticated to receive much confidence. In form all dams were curved, up stream in small dams and down in the larger. This was doubtless due to the current, which in small streams, obstructed easily in the centre, would become stronger on the sides and push the sticks down, while the reverse would be the case in large streams. Ordinarily the dams would support a man's weight. They seemed like masses of driftwood under the foot. The older they were, the more compact. Within the ponds, formed by these remarkable dams, sometimes covering more than fifty acres, one or many lodges were built to furnish shelter and protection to the beaver family. These houses were dome-shaped structures composed of sticks and mud, the dome rising above the water-level between four or five feet and extending along it about sixteen feet. The top of the lodge was left rather loose, but below it was compact with earth. This gave the interior sufficient ventilation. The floor, which was about two inches above the water-line, was hard and clean with, in summer time, fresh cut grass around the sides. Being so near the level the inmates could tell, by the lowering of the surface, whether the dam had a break in it, in which case they would sally forth to make repairs. Trappers took advantage of this trait, breaking the dam and setting traps in the break. The interiors were about two yards in diameter and twelve to sixteen inches in height, the roof above being about three feet in thickness, while the sides were four or five. There were several kinds of entrances, ten to fifteen feet long, but one was always straight with an inclined floor, to permit food sticks to be taken into the house and out again when the bark on them had been consumed. Then the sticks were used in construction work. Other entrances were more abrupt and full of curves. The winter pile of food sticks was sunk alongside the house where it was easily accessible under the ice. No animal could successfully attack one of these lodges, so that the family within it was perfectly safe, but men with axes could force an entrance from above. [Illustration: Beaver Canal. From Morgan's _American Beaver_] [Illustration: Lower Colorado River—Mouth of Gila on Right. Where Pattie Trapped Beaver in 1826. Photograph by Delancy Gill.]