I'll start off by listing my palette. I will list brand names if that color is specific to that brand.
Cadmium Yellow Light
Cadmium Red Light
Crimson Lake (Holbein)
Ultramarine Deep (Holbein)
Cobalt Blue (Utrecht)
Viridian Hue (Holbein)
Yellow Green (Utrecht)
Titanium White (Utrecht or Gamblin)
Here is my starting scene. It's around 4:30pm and the sun is still pretty high. Not much warmth to the light yet.
I begin by toning my canvas with a mixture of cadmium red light and a touch of ultramarine, thinned with Gamsol. A wadded-up paper towel is better than a brush for this, and leaves the surface drier. With a finer bristle brush, I sketch out my composition. That's Camelback Mountain in the distance. It can glow red as the sun goes down, so I really want to contrast that with the dark shape of the shadowed hill. I find that the reflected colors in rocks and mountains can be just as vibrant and change as quickly as clouds in the setting sun. It's a great backup plan for times that a sunset doesn't work out, since we get so many clear skies in Phoenix.
I like to block in the shadows first. Since the color in the shadows won't be changing much as the sun goes down, it makes sense to tackle them right away. The shape of the shadows, however will change significantly. When painting in the afternoon, shadows will keep getting longer. Keep this in mind when working out the composition. Sometimes I will paint the shadows where I think they will be later as the sun moves down.
Shadows and rough shapes have been blocked in. The light still hasn't changed much (see the next photo), so I'm still focusing more of my attention to the main shadow area. In order to keep the eye from wandering off the right edge of the painting, I'm going to paint a saguaro getting full sun overlapping the mountain's cast shadow. The highlights on the distant mountain are gradated from the edge as well, with brighter, orange highlights bringing the eye back towards the center.
The scene in front of me hasn't changed much in the block-in stage. Colors are getting a little bit more golden but that's about it. I'm using this time to paint reflected sky light on the shadowed rocks/ground/bushes.
Next I started working on the foreground. The dark shapes behind the foreground allow for a nice contrast. I considered edge quality, value, and color intensity. A few bright, sharp edges in the saguaro cacti bring the foreground forward. I softened some of the bushes.
As the sun gets lower, warm reflected light from the rocks gets stronger. I refined the clump of boulders to the left and added some subtle color shifts in the shadows. Warm light started accenting foliage, and I added a few brighter yellows to the foreground. Once in a while a Palo Verde branch can be angled just right and reflect very bright light from the sun.
I always save the sky for last, since that changes quickest in an afternoon painting (Opposite when working on a sunrise). Thankfully a few small clouds showed up near the horizon, making the sky a little more interesting.
And here is the finished painting in the field, signature scratched in the wet paint with a toothpick.
Thanks for reading, and happy painting!