There is no obvious explanation however fror the May/20-Jun/10 rally.  That does not mean that there was not an external cause, only that we do not know about it.  From the way price moved, it looks like a few Chinese traders went on buying sprees, one at  a time, mostly in that 20-day period but also in the next 2 months.  My guess is that they got inside information of some future positive development, that prompted them to buy.  But now that expectation has somehow deflated, so they are dumping what they bought. 

Perhaps they expected the international versions of Huobi (BitVC) and OKCoin (OKCoin.com) to start a new bubble (rather disappointing so far).  Perhaps they were XRP owners who heard of Jed McCaleb's plans to sell his billion XRP, expected XRP to crash, and rushed to exchange theirXRP for BTC; only to undo the switch now that Jed struck a deal with Ripple.  Or, conversely, perhaps they were people who wanted to buy Jed's XRP, and stocked up on BTC for that.  os osmething else.