Back in Balboa Park’s Old Cactus Garden for a third week, I turned my easel and looked south. I liked how the morning light lit the plants, the left falling slope, and the contrast of the organic shapes to the distant buildings. I worked quickly from front to back but stopped when I got to the upper left, hesitating to include the angular modern buildings. Was that the kind of contrast I wanted? Would it be distracting? Jarring? In the end, I turned to the north and sketched in the towers from the Museum of Us, which like the Old Cactus Garden, date from just over a hundred years ago, for a more harmonious contrast.