In the late 1960s, Heizer left New York City for the deserts of California and Nevada, where he began making his first "negative" sculptures. These works were created by removing earth to shape subterranean negative forms directly into desert floor. Completed in 1967, North, East, South, West, consisted of several geometrically-shaped holes dug in the Sierra Nevada. The following year Heizer completed "Nine Nevada Depressions", a series of large negative sculptures located primarily on dry lakes throughout the state, Jean Dry Lake, Black Rock Desert and Massacre Dry Lake, near Vya, Nevada among them. In 1969, Heizer made the series Primitive Dye Paintings, in which white lime powder and concentrated aniline dyes were spread over the dry desert landscape, covering large areas that, when viewed from the air, formed amorphous, organic shapes. The culmination of this critical early period was the creation of Double Negative in 1969, a project for which he displaced 240,000 tons of rock in the Nevada desert, cutting two enormous trenches—each one 50-feet-deep and 30-feet-wide and together spanning 1,500 feet—at the eastern edge of Mormon Mesa near Overton, Nevada.