This is the drop chamber for a mostly quiet drain that cuts through the slope of a ravine. The grille at the top seems to be doing its job swimmingly as its designed to catch large pieces of debris, which may cause damage downstream during heavy storms. The warped platform suggests that something, or some things, came down hard enough to bend steel. At the bottom is the deep plunge pool at the bottom is mean to absorb the impact of water and soften the effects of erosion on the concrete floor. From here, the water is able to continue down the conduit at a more controled rate towards the outfall (which is also a bit damaged).