http://history.nasa.gov/SP-168/section2b.htm#118

"The tracks of numerous rolling boulders, some of them more than 100 feet across, are visible in Lunar Orbiter V's high-resolution photograph of the crater Vitello, on the southern edge of the Moon's Sea of Moisture, remarked KENNETH L. WADLIN, of the Lunar and Planetary Programs, NASA. "The picture was taken on August 17, 1967, from an altitude of about 100 miles.

"Two such tracks can be seen in the enlargement at right. The complex pattern of the 900-foot track left by the large boulder indicates that this boulder, which is about 75 feet across, is quite angular. The buffeting that it experienced in rolling did not cause it to break up or become rounded. This points both to the integrity of the material of which it is composed and to the deformable nature of the surrounding surface material.

"The more uniform track of a smaller, more rounded boulder can be seen to the right of the large one. This smaller boulder is over 15 feet across, and traveled 1200 feet before it came to rest.

"The boulders may have been set rolling by moonquakes or meteor impacts."