Although he was always hostile to the development of abstract painting, Edward Hopper's art gives forth a distinctly modern feeling. In 1967, shortly after Hopper's death, James Thrall Soby commented that many of his (Soby's) friends among the Abstract Expressionist painters genuinely admired Hopper's work. "It always astonished me," Soby noted, "that these young artists exempted the late Edward Hopper from their acrimony against the realist tradition." In fact, the mood of loneliness and alienation in Hopper's paintings harmonizes well with the existentialist philosophies of this century, while his compositions always went beyond mere realistic transcription to establish patterns and relationships of abstract form.

Hopper achieved success in watercolor at a time when his oil paintings were still being rejected from exhibitions. He took up the medium in 1923, not having used it seriously since his student days, except in his commercial work, and made a large group of watercolors of old buildings and lighthouses in Gloucester, Massachusetts, and in Portland and Cape Elizabeth, Maine. Late in 1923 The Brooklyn Museum purchased his House with Mansard Roof, the first painting he had sold since the Armory Show. In the following year he was taken up by the New York dealer Frank Rehn, who sold every watercolor on the wall, and five more as well, from the first show he put on of Hopper's work.

Hopper's early watercolors were small and fresh in technique, and he generally completed them in a single sitting. In the 1940s and 1950s, however, in such works as Saltillo Rooftops, he moved to a larger scale and a more calculated sense of composition. He also worked on his watercolors for longer periods, sometimes as much as a month, carefully building up the colors "in a series of glazes," although always with translucent washes and never with opaque pigment. This resulted, as is evident in Saltillo Rooftops, in an extraordinary depth and richness of color, particularly in the shadows, and a new solidity in the realization of form.

While it depicts Mexico rather than the United States, Saltillo Rooftops exemplifies the feeling of provincial desolation that Hopper captured so ably in his work. In the summer of 1943, having no gas to travel from New York to Cape Cod because of war rationing, Hopper made his first trip to Mexico by train. Displeased with the rush and bustle of Mexico City, he spent most of his time in Saltillo and Monterey. The stay in Saltillo proved the most productive, and from the roof of the Guarhado house he made three watercolors in addition to Carnegie Institute's: Sierra Madre at Saltillo (private collection), Palms at Saltillo (collection of Mr. and Mrs. Robert M. Bernstein), and Saltillo Mansion (The Metropolitan Museum of Art) . In 1946 he returned to Saltillo, staying at the Hotel Ariape Sainz, where his room let out onto a large roof terrace from which he could paint. At this time he executed four more watercolors: Roofs, Saltillo, Mexico (Whitney Museum of American Art), El Palacio (Whitney Museum of American Art), Church of San Esteban (The Metropolitan Museum of Art), and Construction, Saltillo (collection of Charles E. Buckley). Roofs, Saltillo, Mexico contains virtually identical mountain silhouettes to Carnegie Institute's Saltillo Rooftops, although the foreground buildings are not the same. In 1951 Hopper again visited Saltillo but apparently produced no work.

Gail Levin, who visited Saltillo in 1983, exactly forty years after Hopper's first visit, found that the scene Hopper recorded in this and other watercolors had remained surprisingly intact, even to the assortment of chimneys and cornices and the sign of the El Palacio cinema that Hopper depicted in the watercolor in The Metropolitan Museum of Art.