The miner pictured in this early 20thc photograph is tending to what is called a sluice. Sluicing, or sometimes referred to as "rocking the cradle," is a method used to find gold. To do this, the sluice is set up on an incline where water can be regulated to flow down into it. Gravel is shoveled into the trough from the top of the incline. Once this process is complete, any gold present will have remained at the bottom of the trough. Gold is discovered by panning out this remaining gravel from the sluice.
H.S. Poley, "Seeking Gold with Water Pressure," (c. 1890-1915), Denver Public Library, Western History Collection, Call Number P-1252.