One of the earliest and most famous contemporary earthworks is the monumental "Double Negative", begun in 1969 (and reworked in 1970) by Michael Heizer. By means of explosives and bulldozers, 240,000 tonnes of earth and rock were displaced from the desert near Overton, Nevada, to cut two opposing slices (9 meters wide, 15 deep, and 457 in length) from the slopes and surface of the Mormon Mesa. These cuts create negative space, and are thus unusual in the realm of sculpture. Traditionally, three-dimensional artworks involve forms created through the addition of materials. This "sculpture in reverse," as Heizer calls it, entails the removal of matter, and generates forms that give viewers the opportunity to occupy the space "inside" rather than just "around" artworks.