This looked like one sizeable market sell that wiped out a large portion of the buy orders on the book, leaving the remaining buy orders starting the way down a

This looked like one sizeable market sell that wiped out a large portion of the buy orders on the book, leaving the remaining buy orders starting the way down at ~$210. This (somewhat predictably) triggered a bunch of people's stops, causing their ETH to be sold at market and pushing the price down even further, triggering more stops, and so on and so on. People should really have paid attention to that not-so-fine print when GDAX added stops because it clearly said that they'd cause a market trade, meaning that if you set a stop to trigger at $250, you would not be guaranteed to get $250, but instead get whatever the highest remaining orders on the book would be. (Disclaimer: I am not a market specialist, I just read carefully before I go clicking on things.)