The sunlight in the middleground was disappearing quickly as the sun moved behind a mountain on my right. I ran upstream to be able to set up in time to capture this sunlight, but keep the waterfall in shadow (so that detail was retained in the highlights of the water). As set up to capture the strip of middle ground light, I was amazed when this cloud came in very quickly from stage left to complete the composition. I took several shots, but I knew when the cloud 'licked' the mountain on the right, my image was complete. This moment lasted a few seconds, before both the cloud became less interesting, and the middleground light disappeared...