"Because there is someone moving around the dam," went on Frank. "I can see one, two, why there's half a dozen men there, Billy!"
"There are?" and the ranch lad galloped up beside his chum. Quickly taking a pair of field glasses from the case at his side, he focused them on the concrete wall.
"That's right," he said, in a low voice. "I wonder what this means? I don't like it, I wish Uncle Richfield was here."
He called to his horse, and increased the animal's speed, and Frank and Andy did likewise. A few minutes later, as the boys galloped across the stretch of land that was in dispute, a man suddenly arose from where he had been sitting on a stone in the deep grass.
"Hold on there!" he exclaimed, and he reached for his gun, which was standing near him. "I wouldn't come any farther if I were you. It might not be just altogether healthy."
"Why—why, what do you mean?" asked Billy, "This is my uncle's land!"
"Oh, is it? Well, I guess not—not here, anyhow!" the fellow jeered. "Now you clear out if you don't want to get hurt!" and he started menacingly toward the lads.
CHAPTER XX
THE BLACK CLOUD
Billy Chase wheeled his horse to bring the animal head on toward the fellow who had warned them away. The man halted, and seemed to be considering matters.