I've been following this story for a few weeks, if not more, and more news has surfaced which seems to have complicated the problem. Here are the two articles I read today concerning the lease issues concerning Robert Smithson's Spiral Jetty.
Hyperallergic:
http://hyperallergic.com/31787/spiral-jetty-updates/
Etsy:
http://www.etsy.com/blog/en/2011/who-owns-spiral-jetty/
And for fun, a video excerpt from Robert Smithson's film about the Spiral Jetty from YouTube:
http://www.youtube.com/watch?v=vCfm95GyZt4&feature=related
