Finally, on September 23, a topographical party went forward to study routes, inquire about wood, water and forage, and select halting places; and two days later some 1400 men, the first section of the "army," advanced into an almost unknown region with about one hundred and seventy-five wagons and provisions for two months.[13.16] The distance to Presidio del Rio Grande, a small Mexican town five or six miles beyond the river, was about 175 or possibly 185 miles. Much of the country proved to be rough and wild, but there were also barren prairies, deep "hog-wallows," rich bottom-land and one fine, broad valley. Several streams had to be crossed, and among these were counted the Medina and the Leona, not less beautiful than their names. Population there was almost none, though on the first day's march Castroville, a German town planted on American soil by a Frenchman bearing a Spanish name, offered quite cosmopolitan suggestions. A drought of several weeks had made the roads hard and the streams fordable, and no serious difficulty was encountered until on October 8 the advance came to the Rio Grande.[13.26] The river was here swift and rather more than four feet in depth; but with the aid of boats and a pontoon bridge, provided beforehand by Wool, the troops effected a crossing safely during the next few days, established a small fort at each end of the bridge--to hold it and to guard the boats for the second section under Colonel Churchill, which was still waiting at San Antonio for the means of transportation--and then camped three or four miles beyond the town for rest and repairs. Some of the teams had come all the way from La Vaca, 330 miles, without stopping for a day. As the small Mexican border force had retired and the citizens were friendly, there was nothing to fear; and Wool's amicable assurances, reinforced with strict orders to molest no one, promoted kind relations. The government had left him without specie, and the people would accept only hard cash; but with private means and by dint of borrowing he obtained half-rations of corn. This brightened the outlook noticeably, for subsistence was to be, of course, the greatest problem; and the arrival here of Brigadier General Shields,[13.17] who brought not only another body of the troops but news that Monterey had fallen, and took command of all the infantry, together with a small force of mounted men, appeared to strengthen the expedition materially.[13.26] [Illustration: WOOL'S MARCH Based on Reconnaissances of Capt. Hughes, Lieut. Sitgreaves and Lieut. Franklin]