The McCarty's Flow is the youngest lava flow at El Malpais and one of the youngest in the continental United States. It erupted from a vent on the northwestern edge of the monument about 3,000 years ago, sending a tongue of basalt almost forty kilometres north along the valley of the Rio San Jose. The surface still looks fresh, with shiny black rope-like pahoehoe textures and almost no soil cover.
There is a viewpoint on Highway 117 with informative panels and an interpretative trail. Pueblo oral histories may contain accounts of the eruption itself — Acoma and Zuni stories speak of a time when the earth caught fire — which would make this one of the only volcanic eruptions in the lower 48 states ever witnessed by people. The flow is fragile and visitors should stick to designated trails.