We spent the first part of last year prowling around the Mojave Desert in southern CA, dirt and gravel roads, and had a lot of flats. These were not fresh type roads, but roads that have been there for a long time. About half of the punctures were in the tread area (these were new AT tires on a Ford Ranger 4wd), the others were in the sidewall, caused when we brushed up against something sharp. Later in the year we were in Alaska, and got two flats on the same tire, couple of days apart, thanks to the graveled streets of Valdez and the surrounding area. I heard of people driving into the Kennicott copper mine area, about 60 miles one way, gravel, who got three flats on the trip. So it seems that gravel and tires don't mix well...