There were at least three perfectly valid reasons why Ford should ride into town that day.

He wanted heavier socks and a new pair of gloves; he was almost out of tobacco, and wanted to see if he could "pick up" another man so that the hours of night-guarding might not fall so heavily upon the crew.

Ford had been standing the last guard himself, for the last week, to relieve the burden a little, and Mason had been urgent on the subject of another man--or two, he suggested, would be better.

Ford did his simple shopping, therefore, and then rode up to the first saloon on the one little street, and dismounted with a mind at ease.

If idle men were to be found in that town, he would have to look for them in a saloon; a fact which every one took for granted, like the shortening of the days as winter approached.
Perhaps he over-estimated his powers of endurance, or under-estimated the strength of his enemy.