The Mistério da Prainha is a lava field extending from the Achada plateau all the way down to the N coast of Pico. It goes back to an eruption in 1562-1564. Unusable for cattle grazing, the area is mostly covered by natural shrub forests and heathlands, here at 600-800 m asl., with species such as Erica azorica or Juniperus brevifolia.