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Indiana University Studies 



First — The inter-mountain plains of the present Departments of Cauca 

 and Valle del Cauca which occupy the first 250 miles of the depression. 



Second — The region of hills and valleys which lie between the two chains 

 along the Cauca River in the Departments of Caldas and Antioquia.The 

 Cauca River, after traversing a portion of the southern plains, flows in this 

 second division of the inter-mountain depression through a series of gorges. 



Third — The river-plain of the lower Cauca, in north-central Antioquia 

 and southern Bolivar, which, bounded by the gradually disappearing spurs 

 of the mountains, soon amalgamates with the great low plain of the Magda- 

 lena River. 



The southern plains (part first, above) area of this inter-mountain depres- 

 sion is divided into three parts: the Plain of the Patia, the Plain of Popayan, 

 and the Plain of Cali. The Plain of the Patia occupies the southern quarter 

 of this area, the Plain of Popayan the next quarter and the Plain of Cali 

 the northern half. The last is thus about 125 miles long and 15 miles wide. 



Of these, the plain of Popayan, with a mean elevation of about 6,000 feet, 

 is the highest, and contains the divide between the waters of the Atlantic 

 and the Pacific. However, there is no marked hill mass between the two 

 drainage basins, such as we had inferred from published maps and accounts, 

 and one of the surprises of the journey was to find that in the Plain of Popayan 

 we had crossed from the tributaries of the Rio Patia, which flows into the 

 Pacific thru a great gorge in the Western Andes at the very southern end of 

 the Plain of the Patia, to the tributaries of the Rio Cauca, which flows into 

 the Atlantic by way of the hill country of Antioquia, without having appre- 

 ciated that we had passed across the hydrographic divide between the two 

 oceans. One would naturally expect in the Andes of South America that 

 the divide between two great river systems, tributary to different oceans, 

 would be a marked mountain crest, and it is perhaps this wholly natural 

 preconception which has led to the showing on a number of maps of such a 

 mountain range across this plain between the head-waters of the two streams 

 and has caused rather misleading statements in many geographic descrip- 

 tions. 



We found the divide to occur here in a rolling plain where the low elevation 

 between the two river systems is of less topographic importance than the 

 elevations between certain tributaries of either river. Looking across the 

 plain from either of the mountain slopes, it would be impossible to say with 

 certainty, in many cases, which little tributary belongs to the Cauca and which 

 to the Patia. The line of this inter-oceanic divide crosses the plain of 

 Popayan in an east-west direction. On the west it mounts to the summit 

 of the Western Andes and then turning abruptly northward, follows it very 

 closely on the western side of the plains area; while to the east it climbs the 

 other chain, and turning abruptly south, follows the summit of the mountains 

 on the east side of the Popayan and Patia Plains. 



There is in this general plains-region the suggestion of a remnant of a 

 cross-range, but it does not lie between the Cauca and Patia drainages, but 

 near the northern end of the Plain of Popayan, and a number of miles north 

 of the head-waters of the northward flowing Cauca. It is somewhat near 

 the boundary between the Plains of Cali and Popayan, but the separation of 

 these into distinct units rests on a marked difference in elevation rather than 

 on this feature. Perhaps at one time in the geologic past this remnant of a 



