In my case, I already had a Chinese visa in my passport and planned the Silk Road trip and made arrangements while already in China, so there was no need to report anything.

However, if it had been my first trip to China and I needed to apply for a visa and wanted to go to Xinjiang, I would have avoided mentioning it in the application itinerary and made up an "alternative reality" trip with bookings that matched, all in eastern China in typical tourist cities. Then cancelled the bookings after receiving a visa. While you don't need a permit and/or prearranged tour to go to most parts of Xinjiang, it is and has been a sensitive place to put on a visa application for quite a number of years now.

I've said it before and I'll say it again here--when dealing with Chinese bureaucracy (of which visa applications definitely qualify), there is the Truthful Answer and there is the Right Answer. If those are in conflict, usually it's best to give the Chinese what they want--the Right Answer--so they can happily process the paperwork and send you on your way, everyone a winner. And once in China, the visa application officer doesn't care about you anymore--you're now someone else's potential headache.