Photograph of Boulder Canyon during construction of the Boulder Dam, showing river between two large mountains, [s.d.]. In the extreme foreground, a large river can be seen extending from the far right to the left. On the far left, the small outline of a shore can be seen. In the background, two large mountain cliffs are visible. The two cliffs frame the path of the river. The river can be seen curving between the two mountains to the right and out of sight. In the extreme background at center, additional mountain ranges are visible.; Description on the side of the image reads: "Looking downstream at the Black Rock site of the Boulder Dam project. The river is almost 280 feet wide at this point and a 550 feet dam would be about 1200 feet wide at the top".