Las Vegas sprawls across a wide bowl ringed with mountains, the Las Vegas Valley, that is drained by Las Vegas Wash. North of the city, the stream runs at the feet of large debris aprons—bajadas—that fringe the rugged ranges on all sides of the valley. Upper Las Vegas Wash has been accumulating sediment for many centuries, leaving a sedimentary record of conditions and ecosystems for millions of years. In today's dry conditions, the present stream is cutting an arroyo into the ancient sediments, exposing a remarkable fossil record from late Pleistocene times as old as about 200,000 years. But casual visitors can be puzzled by what they see here.
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- Setting of the WashComing into the country
- Arroyo BluffsExposing fresh strata
- Arroyo BanksFossils are hidden
- Wash GravelsThe typical sediment of today
- SiltsWith wormy concretions
- BurrowsProbably not fossils
- Packrat MiddenOld or new?
- Freshwater Snail FossilSign of ancient marsh
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