The valley of the Río Sandia (approx. 14° 20′S, 69° 30′W) on the eastern side of the Andes in the department of Puno, Peru is one of several valleys that descend from the high altiplano to the tropic lowlands of the Amazon basin. The cactus flora of the valley is poorly known, generally inconspicuous, yet significant for a number of reasons. It is the type and only known location for Lymanbensonia micrantha (Vaup.) Kimnach and a second locality for the recently described Echinopsis serpentinaM.Lowry & M.Mend. A further Echinopsis species encountered in the valley is herein described as new. Historical records of the cactus flora from the valley are outlined together with contemporary observations based on two visits by the author in 2008 and 2013.