The need to create is innate and universal. No artist better demonstrates this than the outsider artist, who asks nothing for his work other than that it be witnessed.

The outsider artist closest to my heart is Leonard Knight. Formerly a mechanic in the US armed services with no artistic training or experience, Knight has spent the last 30 years or so building and maintaining a 150-foot-tall installation in Niland, Calif., on the banks of the Salton Sea. He calls it Salvation Mountain; you may recognize it from the films Into the Wild and Bombay Beach.

Having learned of Salvation Mountain during graduate school at San Diego State University, I revisited the site over the recent holiday.

It used to be that Knight would greet you at the foot of the mountain with a warm hello before saying something like, "Let me show you what I'm doing over here," and leading you on a tour of the mountain and his two adjacent "museums," all of which he constructed out of adobe, latex paint and found objects.

If you offered to help, he'd say, "No, thank you," then he'd return and say that maybe he had a thing or two you might be able to do. Then he'd fill your arms with Salvation Mountain swag—postcards, puzzles, videos—intended for sale.  

When, in Into the Wild, Emile Hirsh asks Knight, "You really believe in love, then?" and Knight answers, "Totally," that's not scripted. That's just Knight. I was sad not to find him there a few days after Christmas.

In the mid-1980s, Knight's sister told him about Jesus Christ. "God is love," she said. And he decided that everyone needed to hear this message. His first attempt to spread the word of God came in the form of a hot air balloon he stitched together himself out of scraps from a balloon factory, the words "God is Love" sewn across the body in bold colors.

The balloon never quite left the ground, so Knight decided to create a concrete memorial near his last attempt in Niland. He poured concrete on a hillside and just kept going up. He tried to stretch his supply by thinning the concrete with water. A rainstorm easily washed it away.

Knight began rebuilding with adobe, and locals supplied him with bails of hay and cans of paint. He found everything else in the desert. He built his first museum, a small adobe hut full of photos, plaques and awards fashioned right into the walls.

When I first visited in 2006, Knight said he slept in that museum to keep cool—the several abandoned trailers on the site being too hot—and that the second museum, already as tall as the mountain itself, would house his full collection.

As we sat at the foot of the mountain, silently together, a church group drove up in a minivan and asked if it could pray. After a long, thoughtful pause, Leonard finally said that he'd have to pray on it and get back to them, which caused the minister to ask how they would get a hold of him for his answer. "Well, I guess you'll just have come back," Knight said.

Now well into his 80s, Knight lived on the mountain until the state issued him a social worker and finally placed him in a long-term care facility in nearby El Cajon. The state said he has dementia.

On my recent visit, witnesses crawled the grounds by the dozen, and I imagined Knight greeting each of them individually, asking that they witness the outcome of his labors.

The paint on the mountain looked vibrant, but the second and much taller museum remains unfinished. Wide cracks have formed in the foundation, and the paint there has certainly faded. It occurred to me that, without Knight, the mountain may not survive, and maybe it shouldn't: We have to keep some space in our hearts and communities for ephemeral art experiences. I decided that I had visited for the last time.

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