This reading is made up of the kun'yomi readings for 香 and 川 (rendaku'd) and the on'yomi reading for 県. You haven't learned this reading for 香 yet, so here's a mnemonic to help:

If you want to get to Kagawa Prefecture you're going to need a car (か). It's all the way over on Shikoku island, and you won't be able to cross the big bridge without a proper car!