What are the chances of the sheriff running into those cowboys? Let alone the Indian at the end. The evil martial said he wanted to check out the cattle ranches because he knew they would be running out of money and food. According to him people who knew how to ride and nothing else often tried to pick up cash at cattle ranches. So it would make sense to him to check out the area cattle ranches. The cowboys also told him it was a wasteland. Not much thinking would involved in concluding that the natives would be looking for water so it would make sense to him to wait where the water was ( possibly informed by the cowboys ).