Later that year, Heizer began to create “negative” sculptures by cutting directly into the earth. Made in 1968, Heizer’s “Nine Nevada Depressions” series of pieces was located primarily on dry lakes throughout the state, comprising a 520-mile earthwork. Jean Dry Lake, south of Las Vegas, has totally absorbed Heizer’s “Rift 1”, a zig-zag trench dug into the lake surface in 1968, as the first of the “Nine Nevada Depressions”. “Dissipate” consisted of five small trenches lined in wood, inserted into the playa at the Black Rock Desert. “Isolated Mass/Circumflex”, the ninth piece, is a circular loop made in a dry lake bed surface at Massacre Dry Lake, near Vya, Nevada. Heizer displaced 6 tons of earth, making a one-foot-wide trench, 120 feet long, with the loop being 12 feet in diameter. This culminated in the production of Double Negative in 1969 and 1970, 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.