Curiously, along the coast of the Caribbean, northeast of the mouth of the Magdalena, is another seemingly independent range of mountains, detached from the East Cordillera and quite in line with the Central: the Sierra Nevada de Santa Marta, which has snow crowned summits rising 16,000-17,000 feet above the sea. The entire mountainous region of Colombia is subject to earthquakes, which, however, are less severe than those in Ecuador and Venezuela; in some sections there are volcanic disturbances.
Plains
Between the mountain chains, besides the narrow valleys are limited plateau regions, the latter occupying about 900 square miles; while more than half of the country, an immense tract east of the Andes, broadening towards the southern boundary, is a great plain slightly inclining towards the east and south: the northern part belonging to the Orinoco Basin, the larger section at the south to that of the Amazon. This Amazon region has an area equal to that of the entire State of California. Its higher portion, as well as most of the Orinoco Basin in Colombia, where there are wet and dry seasons, is composed chiefly of grassy plains called llanos. Nearer the Amazon, where it rains a good part of the year, the country is heavily forested.
Rivers
Rivers entering the Caribbean Sea. Most important at present as also best known are the rivers which flow into the Caribbean Sea. Chief of these is the Magdalena, 1020 miles long, the principal route to the interior. The most important affluent of the Magdalena is the Cauca, which enters it about 200 miles from the sea, after descending nearly 15,000 feet in a distance of 810 miles. The Magdalena has many other tributaries, 500 or more, a few of which, entering from the east, are navigable for small steamers. The Atrato River, 340 miles long, flows north between the highlands of the West Cordillera and the Coast Range, later turning east into the Gulf of Urabá. Of smaller streams flowing into the Caribbean, the Sinú bears considerable traffic. Besides these, there are the navigable Zulia, 120 miles, and the Catatumbo, 108 miles, which by way of Lake Marcaibo in Venezuela also enter the Caribbean.
Rivers entering the Pacific. Into the Pacific flow many streams carrying much water, as the rainfall of the region is excessive; but the courses are mostly so short and the fall is so steep that few are navigable for any considerable distance. The longest of them, the Patía, 270 miles, is the only one which rises on the east side of the West Cordillera. Worth noting is the fact that this river and four others, the five belonging to three different basins, rise very near together in the highlands of southern Colombia; the Cauca and Magdalena going north to the Caribbean, the Putumayo and Caquetá southeast to the Amazon. The Patía penetrates the West Cordillera by a remarkable gorge with perpendicular walls several hundred feet in height. On the swampy lowlands the river channels are navigable. The San Juan River, 180 miles long, is navigable for 140 miles, as it, like the Atrato, flows a long distance parallel with the coast between the Baudó Range and the Cordillera, until it turns west into the Pacific.
Amazon Tributaries. The Amazon receives two large tributaries from the southern part of Colombia: the Putumayo, 840 miles; and farther east the Caquetá, 1320 miles, the last also called the Yapurá, especially in Brazil. These rivers are navigable by canoe and by steamers of shallow draft for hundreds of miles, though with interruptions in places from difficult rapids. The Putumayo is the better, having been ascended a distance of 800 miles from the Amazon in a steamer drawing six feet. (The entire length of the Hudson is 350 miles.) Smaller rivers, the Guainía and the Vaupés, unite with the Casiquiare from Venezuela to form the Rio Negro, another important affluent of the Amazon. These rivers have many smaller tributaries, but the section has been little explored save for going up or down the main stream.
The Orinoco River, which part of the way forms the boundary between Colombia and Venezuela, receives several important tributaries from the former country: the Guaviare, 810 miles long, the Vichada, 312 miles, the Meta, 660 miles, and the Arauca, 480 miles. Though all are more or less navigable the Meta is the most important. Joining the Orinoco below the Maipures cataract and the Atures rapids, which higher up obstruct the greater river, it permits continuous navigation to the Atlantic Ocean. Where joined by the Meta the Orinoco is a mile wide. The Meta is navigable for 150 miles above the junction, in the rainy season 500 miles, to a point but 100 miles from Bogotá.
Climate
It has already been noted that the altitude of a district as well as its latitude affects the climate, which may be modified further by the direction of prevailing winds and by ocean currents. The extensive and lofty mountain ranges of Colombia therefore give the country a greater variety of climate than it would otherwise enjoy, with temperatures agreeable to every taste and suited to products of almost every character. The configuration of the mountain ranges and valleys causes a further difference in temperature and in rainfall among points at the same altitude; the elevations being responsible not only for their own lower temperatures, but for the greater heat of secluded valleys, and for other variations.