I explored some new areas of Papago Park this morning. I found an old saguaro in a small wash, and the morning light hit it in just the right way. It was mostly cloudy which kept me cool. The sun came out now and then, and I used that opportunity to place the highlights. Since the clouds are moving and the light can go away quickly, it's a good idea to take a mental "snapshot" of the light, that way you can continue painting highlights after the light fades.