The Rangers, still overshadowed by that pall of yellow dust that seemed inseparable from them, and almost as much a part of themselves as their horses or accouterments, dashed gallantly out of the town and across the rather dreary expanse of mesquite and thorny cactus that lay between San Mercedes and the Rio Grande. On the brink of the stream, which at that point flowed between steep bluffs of a reddish hue, they drew rein. The boys peered curiously over the bluff on the edge of which they had halted. They saw a shallow, slowly flowing stream obstructed with sand bars and shallows. On its banks grew scanty patches of brush and dull–colored, stunted trees; but the scene was a dreary, almost melancholy one. “So this is the Rio Grande!” exclaimed Ralph, in a disappointed voice, “I always thought of it as a noble river dashing along between steep banks and————” “Gracious, you talk like Sir Walter Scott,” grinned Jack; “the Rio Grande at this time of the year, so I’ve been told, is always like this.” “Why, it’s not much more than a mud puddle,” complained Walt Phelps. “I’m not so sure about that, young men,” put in Captain Atkinson, who had overheard their conversation, “at certain times in the early spring, or winter you’d call it back east, or when there is a cloud burst, the old Rio can be as angry as the best of them.” “What’s a cloud burst?” asked Ralph curiously. “I’ve read of them but I never knew just what they were.” “Well, for a scientific explanation you’ll have to ask somebody wiser than me,” laughed Captain Atkinson, “but for an everyday explanation, a cloud burst occurs when clouds, full of moisture, come in contact with mountain tops warmer than the clouds themselves. This causes the clouds to melt all at once—precipitation, I believe the weather sharps call it—and then if you are in this part of the country, look out for squalls along the river.” “But I don’t quite understand,” remarked Walt. “I guess I’m dense or something. I mean there are no mountains here.” “No; but up among the sources of the Rio there are,” explained the leader of the Rangers, “and a cloud burst even many hundred miles away means a sudden tidal wave along this part of the Rio.” “Well, it certainly looks as if it could stand quite a lot more water without being particularly dangerous,” commented Jack. At this point of the conversation Captain Atkinson gave a quick look around as the rumble of approaching wheels was heard. “Here comes the chuck–wagon, I guess,” he said; “you boys will have to excuse me while I ride off to tell them where to make a pitch.” “Yes; I suppose a chuck wagon naturally would make a pitch,” grinned Ralph, as Captain Atkinson clattered off. “The kind of pitch he means is a location,” rejoined Walt Phelps. “Look, boys! there she comes. Well, that means that we don’t starve, anyhow.”