abstract
| - Xépôn was located on the north bank of the Sepon River at an altitude of . The countryside was mountainous, broken, and covered in subtropical forest. Average rainfall each year was . In the rainy season (July to September), rainfall could be a month. The Sepon River runs in a trough between two natural, high ridges. The trough itself is only wide. This geologic feature begins just west of the town of Khe Sanh in Vietnam. The northern ridge ends near Xépôn, while the southern ridge continues for another . A shallow bowl forms between the ridges (permitting north-south traffic out of the valley) near the Laotian town of Ban Dong. The southern ridge turns southwest (followed by Route 9 on the north side and the Banghiang River on the south side), and ends near the town of Mường Phìn. However, the best break in these ridges occurred at Xépôn, where land traffic could move east, southeast, and southwest.
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