Aerial view from the south showing the Smithsonian Institution Building with the United States National Museum, now the National Museum of Natural History, across the Mall. South of the SIB are visible the Astrophysical Observatory sheds, the South Shed, and the elongated Quonset hut-like Air Shed. The South Yard is flanked on the left with the Freer Gallery of Art, opened to the public in 1923, and on the right with the Arts and Industries Building. On the right are temporary buildings erected during World War I and behind them is Center Market. The Mall is landscaped with winding footpaths and dense clusters of trees, reminiscent of Andrew Jackson Downing's 1851 plan for the Mall grounds. In the early 1930s the Mall was leveled and the trees cleared as part of the McMillan Commission's efforts to return Washington to the L'Enfant plan.