Hoover Dam. This concrete dam is located on the Colorado River, in Black Canyon, on the border between Nevada and Arizona, USA. It is over 200 metres tall, holding back the waters of the reservoir behind it (Lake Mead). It was built between 1931 and 1936. US Route 93 crosses the dam. Also visible are numerous pylons and cables that distribute the electricity generated by its hydroelectric power station. The white 'bathtub ring' around Lake Mead behind the dam shows the effects of drought in the western USA. The lake is nearly 30 metres below its maximum level. Photographed in March 2013.