National parks always make for great nature porn, but the photos taken at the Grand Canyon this weekend are uniquely breathtaking. In what the Grand Canyon National Park, on its Facebook page, referred to as a "once in a lifetime, outstanding, crazy, amazing, mind blowing" temperature inversion, the gorges on Friday filled entirely with rolling clouds of fog. About 4.17 trillion cubic meters of it.

Park rangers, apparently, wait years to catch sight of the inversion. While it can occur once or twice a year, it usually only fills the canyon partially, or else happens on cloudy days. Ranger Erin Whittaker told the Daily Mail that Friday was like a "really awesome beach day" for the people who work there, with everyone abandoning their posts to check out the sight. Tourists, not realizing how special the event was, complained that the regular view of the Colorado River was blocked.

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And just as the rangers were telling us how rare of a moment we'd missed, it happened again on Sunday. Below, check out some of the best photos taken from the rim's edge:

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