Older lava flows have pahoehoe surfaces with lava tubes and pressure ridges, while Holocene flows are more commonly aa lava with blocky surfaces. Some flows have reached the Rio Grande River west of Payún Matrú, damming it; the river later cut through and formed table-like landforms and canyons. One of these is a slot canyon known as La Pasarela, where the structures of lava flows such as joints in the rocks and vesicles are clearly visible. The entire field covers an area of over and some of its flows have reached the Llancanelo Lake north of Payún Matrú and the Salado River in the east. The estimated volumes of the entire Payún Matrú volcano are as large as ; the volcanic edifice was generated mostly through Strombolian and Hawaiian eruptions.