Río Los Sauces is a tributary of the Río Ñuble located in the Ñuble Region of Chile, draining a tight gorge valley that sees relatively little paddling traffic compared to better-known runs near Pucon. Because this drainage receives considerably less precipitation than the rivers around Pucon, the best window for paddling is during spring — November through December — when snowmelt provides adequate flows. Paddlers arriving outside this window may find levels too low to be worthwhile.

Access to the river requires driving east from the Panamericana at the town of San Carlos toward San Fabian de Alico, a journey of roughly 45 kilometers, only about half of which is paved. From San Fabian, an additional 30 kilometers of rough road heads up the Ñuble valley before reaching the road's end at a hanging bridge over the Río Los Sauces. The road up the valley above the gorge is steep and was relatively recently constructed. A van or vehicle with reasonable clearance is advisable given road conditions.

The character of the run is predominantly class 2, with rapids picking up noticeably in the final 3 kilometers before the take-out. Some of those lower rapids have been described as fun while others are more demanding. The river flows through a tight gorge for a portion of its length. Just downstream of the pedestrian bridge at the put-in, there is a low-volume, junky class 3 rapid that is out of character with the rest of the river.

The valley retains a remote, working-rural character. Chilean farming families have lived in the area for generations, tending sheep, and paddlers have found them welcoming. The confluence of the Río Los Sauces with the Río Ñuble serves as a reference point for trips that continue downstream on the Ñuble, and the Los Sauces pedestrian bridge is also used as a staging point for multi-day expeditions into the upper Ñuble drainage. Basic food supplies can be purchased in San Fabian before heading up the valley, but amenities beyond that are limited.