He gave you a check; and everyone who was there knew he would hurry up to Crater and stop payment on it, if he could do it and keep out of your sight.

Those cronies of his would do the same--so they paid with checks.
"And the Catrock gang knew that.

They mean to get hold of you, rob and-and-kill you, and forge the endorsement on the checks and let one man cash them in Crater before payment can be stopped.

Indeed, the gang will see to it that Jeff stays away from Crater.

Lew hinted that while they were about it they might as well clean out the bank.