Battery jumps from 57% to 0% then back to 50% an hour later

I was hiking in the Wasatch national forest. A friend and I where hiking on Quartzite rock (giant slab) and I pull out my iPhone 5 running ios7 to take a picture. I have 57% battery and suddenly my phone powers off and won't turn back on and says it needs to be plugged in. My friend's iPhone 4 running ios7 (it might be a 4S) also powered down and indicated it needed to be charged. We continued up the rock for a while and on our way back down the mountain, a decent way after the spot where the iPhones stopped working we pulled out our phones and they turned on.

Is this just a coincidence or are iPhones subject to interference from natural elements that would result in behavior like this?

Thanks for any insight!

-Jim