I enjoyed cross-country road trips. And I found the work challenging because it was art that existed on the land rather than mere concepts in a gallery or photographic documentation, or any of the paraphernalia that can be used to indicate that. The art was on the land.

Art wasn't for selling. Actually, we once did have an offer on Double Negative. Things could be sold actually - everything could be for sale. But we had very few buyers. I think it was Michael Heizer who said that the point was to have a bigger canvas, and I've used that expression quite a bit. But I was thinking today that a canvas has boundaries; it has limit to it. And for earthwork, it was the very openness and feeling that there were no boundaries that made it so exciting.

Making the effort is quite a pleasure in itself.

I remember very vividly. I was here in New York. Nancy Holt called me and - I feel unhappy thinking about it - she said that Bob Smithson had died. I said, "Oh, Nancy, what will we do without Bob?" He was a very good friend.

There's a definite connection in terms of objects at hand - dealing with objects or material at hand. Pop art was very much enamored with popular imagery, and popular imagery was of course available and at hand. And land art was also using what was at hand.

I myself had lived in the San Fernando Valley many years ago, when it was a much wilder place, and we used to go walking in the wild areas. So that early experience had a lot of similarities for me to the places that Double Negative was being done.

I think that Walter De Maria's Lightning Field, Michael Heizer's City, and Charles Ross's work in Star Axis New Mexico , all three will last for a millennium.