All of the paintings that he completed for the Bureau of Reclamation are watercolors, however, Jackson is probably better known for his oils of the Midwest. After beginning in printmaking, specifically woodcuts and lithographs, he made the shift to painting with Still Life with Postage Stamp in 1955. The expressionism and flat, two-dimensional, patterned prints of his earlier years gave way to increasing naturalism. Realism as a reaction against Abstract Expressionism gained a significant following starting in the late 1960's, the most visible of the movement being the photo-realists and the super-realists, artists such as Richard Estes and Chuck Close. While Billy Morrow Jackson was certainly painting in a realist manner, his use of ambiguity (imperfect or rough lines, for example) and his beautiful use of light for compositional purposes also linked him to the historic American Luminist school of the 19th century. The Luminists tended to depict landscape scenes (in the tradition of Constable and Turner) with a romantic sensibility, much like Jackson was doing. The sky is a dominant feature in many of Jackson's paintings, pushing the horizon line down towards the bottom of the canvas. The empty fields and solitary farm houses impart a sense of vastness and expanse that is enhanced by his use of perspective. Some of Jackson's later works moved indoors, where he exploited walls and doors to impart depth as well as employing perspective. These later paintings were also infused with a beautiful sense of light. Jackson's paintings recall the paintings of Andrew Wyeth and Edward Hopper in their use of realism to convey feelings of isolation and vastness.
The paintings that Jackson did for the Bureau of Reclamation are more representational than some of his other works. The other paintings may be realistic, but there is a sense of the artist choosing a vantage point from which to make a statement. For the Bureau of Reclamation's watercolors, the choice of viewpoint seems to be more a question of how to fit as much of the dam into the painting as possible. He still uses watercolors beautifully, the shadows on the dam in Shasta Dam or the water in Trinity Powerplant and Whiskeytown Lake show his mastery of this medium. Of these paintings, Whiskeytown Lake is the most impressionistic and the one that conveys the most feeling in his treatment of water. There are some humorous touches, such as the running water fountain in the lower right-hand corner of Shasta Dam, clearly paralleling the flow of water over the dam itself.