Low water in Green River, Canyon of Desolation. Utah.
USGS Earth Science Photographic Archive digital file: hjk00752

Note the low level of the Green River in these Rapids. Powell's brother-in-law, the "Professor" Almon H. Thompson got the job of leading the Second Expedition through the canyon during the heat of August, 1871. Low water meant more rowing, dragging, and portaging the boats downstream through the generally shade-free canyon. Note the steep, blocky talus cones that extend from the cliff face directly to the river in many of the images. For much of the canyon there is little room for plant communities to become established along the canyon bottoms.