Many streams in southern Arizona are either ephemeral (they only flow a small part of the year) or intermittent (the water is disjointed during dry seasons with pools of water separated by dry stretches, often connected by underground flow). Many of those same streams are also partly or completely lined with bedrock, a solid layer of rock over which the water flows. In bedrock-lined streams, the water doesn’t soak into the ground during dry periods and instead sits on top of the rocks as shrinking pools:
These pools are called tinajas (tih-NAH-hahs) and are very important to many desert aquatic insects. In fact, they are often the only reason many insects survive until the rains return and flow is restored in the stream. They are absolutely full of life!