Same thing sort of happened to me riding out in the Hamptons last week. In trying to reach the beach while staying as long as possible on a road with a nice bike lane, I detoured onto a road that looked like a good shortcut between the two main N/S routes, the second of which had no bike lane at all and that I wanted to spend as little time on as I could. (I knew this road came out the other side as paved, as I had seen it many times.) About a mile in the pavement went away. Not too bad, packed gravel. Then it turned to loose sand...with 25mm tires. Urgh. Paved on both ends, MTB territory in the middle. Had to go back north through a development to stay on pavement. Added a couple mile to the trip, all told, so not so bad, but still surprising.