with Sam Francis, using colored skywriting smoke and cloud seeding materials. A pivotal environment Turrell developed from 1969 to 1974, The Mendota Stoppages, used several rooms in the former Mendota Hotel in Santa Monica which were sealed off, with the window apertures controlled by the artist to allow natural and artificial light to enter the darkened spaces in specific ways. Roden Crater In 1979 Turrell acquired an extinct cinder cone volcano located outside Flagstaff, Arizona. Since then he has spent decades moving tons of dirt and building tunnels and apertures to turn this crater into a massive naked-eye observatory for experiencing celestial phenomena. A completion date for the Crater has been announced and pushed back several times since the 1990s. The last time Turrell or his team went on record talking about a completion date, the goal was 2011; but according to a 2013 article in the Los Angeles Times, "nobody volunteers a date any more". Roden Crater has been long shrouded in secrecy and access limited to friends of the artist, although fans have sneaked in without the artist's permission. More recently, a program was established by which devoted fans can gain sanctioned access by completing the "Turrell Tour", which involves seeing a Turrell in 23 countries worldwide, and during May 2015, Roden Crater was open to a select group of 80 people at a cost of $6,500 per person.<ref>{{cite news|last1=H. Miller|first1=M.|title=James Turrell Allowing Limited Visitors to Roden Crater for $6,500 a Person|url=http://www.artnews.com/2015/02/19/james-turrell-allowing-limited-visitors-to-roden-crater-for-6500-a-person/|access-date=January 27, 2016|publisher=ARTnews|date=February 19, 2015}}</ref> Although he works in the American desert, Turrell does not consider himself an earthworks artist like Robert Smithson or Michael Heizer "You could say I'm a mound builder," he said. "I make things that take you up into the sky. But it's not about the landforms. I'm working to bring celestial objects like the sun and moon into the spaces that we inhabit." He added: "I apprehend light—I make events that shape or contain light." Skyspaces In the 1970s, Turrell began his series of "skyspaces" enclosed spaces open to the sky through an aperture in the roof. A Skyspace is an enclosed room large enough for roughly 15 people. Inside, the viewers sit on benches along the edge to view the sky through an opening in the roof. As a lifelong Quaker, Turrell designed the Live Oak Meeting House for the Society of Friends, with an opening or skyhole in the roof,