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The only difficulty which the caravans encountered on the roads over the plain was the crossing of the rivers. They were forded. Fords with a muddy bottom on the lower course of the rivers, such as that on the Saladillo near the confluence of the Rio Tercero, were more difficult for wagons than the fords with sandy bottoms in the upper course, near the fringe of the mountains, such as those of the Rio Tercero on the Córdoba road, or of the Rio Cuarto on the road to Chile. After rain, certain parts of the plain are flooded and impassable. That is the case in the district to the south of the lower Salado, at the very spot where Père Cardiel notices the lack of water in the dry season (1747). The direct road from Buenos Aires to the sierras was at that point exposed, alternately, to drought and flood. The line of the Southern railway, which crosses this low district, is still cut periodically on both sides of Las Flores by floods. The lack of an organized network of streams, the irregularity of the rains, the difficulty of ascertaining the inclination, and the flow of the waters over a plain which seems to the eye to be perfectly level, have led to more than one miscalculation on the part of the railways, which were constructed hurriedly, and before the general survey of the Pampa was finished. Some lines, on the Pampa or on the Chaco, have had to be partially reconstructed, and raised higher, after a series of rainy years.[106]

The colonization of that part of the plain which actually constitutes the province of Buenos Aires was late. It belongs to the era of the railways. There is only one historic road crossing this area, which remained until the last third of the nineteenth century in the hands of the Indian tribes. This is the salt road. We do not know exactly when it began to be used. In the eighteenth century, in spite of the competition of salt from Cadiz and Patagonia, imported by sea, the Pampa salt was the main part of the supply of Buenos Aires. The salt road was not abandoned until after 1810. We still have the diary of several journeys from Buenos Aires to the salt-pits. They were military expeditions. Hundreds of wagons, with a strong escort, collected at Lujan and Chivilcoy, and they reached Atreuco, west of the Guamini and Carbuë lakes, after a fifteen to twenty-five days' march.

The itinerary was fixed in detail. In 1796 D'Azara noticed the wells sunk by the salters, north of the Palentelen lagoon (Bragado), when they found the lagoon dry. From Palentelen south-westward the salt road followed the track used by the Indians of the south-west in their expeditions against the ranches of the Buenos Aires frontier. Near Lake Epecuen, north of Carbuë, it was joined by another track which came from Olavarria, the stages of which were marked by the streams that came from the Sierra de Curumalan. The Carbuë district, the cross-roads of the tracks, was one of the places where the tribes collected. "This place," says the diary of the 1778 expedition, "is the first point where the hostile Indians meet and rest when they leave the Sierra and on returning from their invasions. They not only rest there, but have their winter pasture there" (in the dry season).[107] Zeballos has described the Indian track, the rustrillada, between Epecuen, Atreuco and Traru Lauquen, where the travesia on the road to Chile began.[108] It was not less than 1,000 feet in width. At the foot of the dunes there were deep parallel grooves made by the feet of the raided cattle, which were taken away by the "Chileños."

The two main roads of the colonial period are the roads to Chile and Peru. On leaving Buenos Aires there was one road for a distance of about 320 miles. The "trade road" passed through Lujan, Areco and Sauce, and reached the Carcaraña, or Rio Tercero, at Esquina. It therefore kept at some distance from the Paraná (32 to 16 miles), on the tableland, crossing the valleys which were embedded in it and represented so many bad parts. It then ascended the Tercero on the right bank as far as the Paso Fereira, at the spot where Villa Maria is to-day. At Esquina de Medrano (Villa Maria) the road to Chile branched off to the south-east, reached San Luis by following the Rio Cuarto, going through Achiras and San José del Morro, and, after a travesia seventy-eight miles in length, came to the Rio Tunuyan at La Paz, and ascended the river to Mendoza.[109]

From Esquina de Medrano the Peru road made for Córdoba in the north-west. From the tablelands which continue the Sierra de Córdoba northward it descended toward the Rio Dulce, which it reached west of Atamisqui, and which it followed as far as Santiago del Estero, where it crossed to the north bank. It crossed the Sali in the latitude of Tucumán, and, passing through Tracas and Metan, followed the depression which separates the Andes from the sub-Andean chains. From Salta it went north to Jujuy, and passed through the Quebrada de Humahuaca to reach the Puna.

The influence of rivers is not much seen in the scheme of the primitive roads. There were in the sixteenth century many routes from Peru to the Paraguay, across the Chaco, but not a permanent road in the strict sense. In the eighteenth century there was a direct road from Santa Fé to Tucumán, by the north of the Los Porongos lagoon and the course of the Rio Dulce. There was another from Santa Fé to Córdoba. These roads were not exclusively used for conveying cattle. The river route which they joined at Santa Fé provided them with a certain amount of traffic coming from the higher provinces. Paraguayan maté reached the Andean regions by this road, and in return the boatmen at Santa Fé loaded up with the wines and dried fruit of the Andean provinces to take to Asunciôn.