I didn't know Michael Heizer until I was preparing for my "Earthworks" show in 1968, and somebody called and told me to look at his work. Heizer had already made land art before any of the others and was deeply into it. But he was very young and working out West, so I wasn't aware of his work until he came and showed it to me.

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.

People tend to view land art as something that happened at a certain historical moment - like minimal art, which I was also very much involved with. But it still goes on. It's very much alive.

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.

The gallery closed its doors in 1971. I could no longer psychologically handle the needs of 12 artists. I cared about all of them, and what was happening with their careers. I'm just not a person who can do that indefinitely. And tax-wise I was concerned because they gallery wasn't making money; it was losing money.

I think the four land artists I showed all worked within a few years of each other. And they were standard bearers, I suppose, for land art. They each did very separate things. Apparently, later in California, a lot of artists started working in that medium and there was something of a rush of earthworks. But I wasn't involved with that.

I think Michael Heizer and Walter De Maria had a love-hate relationship because they both had a lot in common. But inevitably one would get more publicity than another. Of course, Robert Smithson's gotten so much attention through the years. One of the reasons is not only that his work is quite wonderful, but the fact that he was a writer himself.