When artist Michael Heizer’s Levitated Mass—a 340-ton granite boulder perched above a cavern of “negative space”—was installed at the Los Angeles County Museum of Art (LACMA) in 2012, the reaction of more than a few people was, “It’s just a rock. How can it be art?” Two years later, director Doug Pray presents a kind of response in his documentary Levitated Mass.

The film, now playing in L.A. and expanding to other cities soon, tracks the installation from the discovery of the boulder at a Riverside, California, quarry in 2005 to the opening of the work on LACMA’s lawn. Along the way, Pray weaves in a brief yet substantive profile of Heizer, his career as a land artist, and his first, abandoned attempt to mount Levitated Mass in 1968. The director clearly respects Heizer’s art and its impact on American culture. He speaks to museum directors, curators, and other creative types who unilaterally praise Heizer’s work and its scale. But the documentary is not an aesthetic defense of Levitated Mass. What makes Heizer’s sculpture art—indeed what’s crucial to all art—is its capacity to move people. And Pray potently captures this power—not at LACMA, but when the boulder is being transported to the museum.

As crews moved the rock from Riverside to L.A. on a specially-rigged, 206-wheel tractor-trailer, a carnival-like atmosphere followed its 105-mile journey. Over the course of 10 nights, thousands of people turned out to see the two-story boulder wrapped in packing material. Some waited hours on highway shoulders, others lined sidewalks and held their babies high to see the boulder creep through their town. Twenty thousand people celebrated at a “rock party” in the small town of Bixby Knolls. When it stopped in Compton, residents took photos with the rock as it waited to continue the trek. If a boulder were going to be a celebrity, of course it would happen in Southern California.

But Pray also captures a different, more interior reaction along the route. Along with the skeptics and conspiracy theorists denigrating the rock, there are people who are inexplicably touched by this epic chunk of the planet and the Herculean effort it takes to move it. A few people weep at the sight of it, while others feel lifted. One man along the route compares it to a lodestone and says people are attracted to it “because it’s energized.” The community of Carson finds divinity in the boulder when an unscheduled stop brings it to rest in front of Roca de Salvacion church. If a boulder is going to be imbued with heavenly meaning, of course it should happen in the City of Angels.

It’s easy to watch these moments with skepticism and ironic detachment. But Pray presents them patiently and reverently. We spend more time with people trying to articulate the impact proto-Levitated Mass has on their core than anyone not directly connected to the work. And as they grapple with their response, we find something stirring within ourselves. Whether that’s empathy or epiphany is beside the point. The boulder has moved people—some to party, others to reflection—and their response reflects back to us, forcing a reconsideration of our preconceptions of Heizer’s work.

Pray’s Levitated Mass is a vital document of the creation of a great piece of art. But it’s the examination of what makes art great, the intangible elements beyond aesthetics, where the documentary becomes invaluable. The boulder clearly has the capacity to inspire, even in its unfinished form, and Pray fundamentally alters the conversation of “why” by allowing normal people—those who visit museums rather than run them—to be the ones to explain its impact. It’s easy to dismiss something challenging when we feel it’s being foisted on us by the elite. It’s something altogether different when the champions are our neighbors, relatives, and friends.