From Calingasta the river flows eastwards feeding the Los Caracoles, Punta Negra and Quebrada de Ullum Dams (Embalse Quebrada de Ullum) located near San Juan city, from which it continues south-eastwards receiving a few more tributaries, including the Mendoza River, to later join the Desaguadero River near the Salina Pampa de las Latas (or Salina Bermejo), at the common border of the provinces of San Juan, Mendoza and San Luis.

The Ullum Dam is 768 metres (2,520 ft) AMSL with a reservoir covering an area of 32 square kilometres (12 sq mi) and a volume of around 440×106 cubic metres (1.6×1010 cu ft).

The upper course of the river is used for water sports such as rafting and fishing, and windsurfing and swimming at the Ullum Dam.

Along its entire length, the San Juan River is heavily used for irrigation.

Media related to San Juan River (Argentina) at Wikimedia Commons