Having been traveling a different route than was normally traveled, when the expedition reached the San Luis Valley, where the dust of 800 men and nearly 2400 horses would easily been seen by Comanche scouts in the Sangre de Cristo (Blood of Christ) Mountains, Anza switched their daily marches to night time travel.  His brilliance as a military strategist, although not mentioned in the diary, is evident by the fact that the expedition's arrival in the San Luis Valley corresponded with the coming of the full moon.  Under its light they could easily see to travel, but their presence would not be detected by the Comanches.