How Chinese forces concealed their Korean War deployment

How did the Chinese People's Volunteer Army conceal its movement toward Korea from the United States?

US surveillance did not overfly China, and infantry-first movement blended into the large volume of supplies already crossing toward North Korean forces.

American surveillance aircraft were not overflying China, so they were watching from the wrong places for the movement that mattered. Heavy traffic already supported very large forces near the border, giving additional columns and supplies background activity in which to hide. A mostly infantry force also created less distinctive movement than a heavily mechanized deployment. Infantry entered first, while other equipment followed through supply flows that could resemble routine support for North Korean forces.