Mr.Rush wins the prize. Yes this is Boulder Gorge on the SVRy. This tank a little unique with regard to it's water source which was up the canyon across the river as shown in Ph 4. In the early days there was a trestle work that carried the feed pipe across. Later photos no longer show the trestle work, so perhaps they dug the line in under the river bed during the fall when water in the river was low. There are some remains of the water intake across the river up the canyon such as boards, screen and some pipe. Here is a Hank Griffith's photo of the location in 1939 from the PNW Chap. NRHS col.