On bed with Michael Heizer in Munich (#2)

Circular Surface Planar Displacement Drawing, Jean Dry Lake, 1970

Earth, 900 x 500 feet. Collection: Sam Wagstaff 

(Zdenek Felix, Michael Heizer, Ed. Fourcade, New York, 1979, p.20)

In 1970, Heizer finished Double Negative and also executed two large playa drawings. Leasing surface rights from the Bureau of Land Management, he directed motorcycles in a series of circles on Jean Dry Lake [1]. Circular Planar Displacement Drawing and Tangential Drawing [2] were documented extensively both from the air and from a scaffold erected specifically for that purpose. The twenty-four-foot tower was built on wheels and moved sixteen feet at a time along one of the four-hundred-foot-diameter circles in order to photograph continuously its circumference.[3] 

—William L. Fox (2002)

Related link:

On Line: Drawing Through the Twentieth Century (MoMA, 2010)
Tangential Circular Negative Line (2012)
On bed with Michael Heizer in Munich (#1)
Walter De Maria, Munich Earth Room (1968)

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[1] It is not sure that several motorcycles were necessary for  the making of these earth-drawings. 

[2] A work reenacted in Munich (Germany), in that same year.
[3] Playa Works: The Myth Of The Empty, University of Nevada Press, 2002, p.36.