Either Townsend or the Spectacle Man had kept the Overland Riders under observation a good part of the time.

It was Townsend who rescued Hippy from the Spurgeon gang, who conducted Hippy back to his camp, and who left the mysterious notes for the Overlanders.
"Yes.

But why did they mark me for the slaughter ?" demanded Hippy.
"Don't you understand?
They thought you were Jim Townsend.

In fact, the mountain men had been informed that Townsend was on his way here as a member of the Overland Riders, to get evidence against the moonshiners.
As a matter of fact, Townsend was already here and had been, in disguise, for some time.

That belief involved our entire party, you see, and it is a wonder that the mountaineers did not get one of you, at least.