Provenance
These questions are associated with a National Geographic article written by Robert Kunzig Feb 2008:
http://ngm.nationalgeographic.com/2008/02/drying-west/kunzig-text/1
The NG article is based on a peer-review publication:
Meko, D.M., Woodhouse, C.A., Baisan, C.A., Knight, T., Lukas, J.J., Hughes, M.K., and Salzer, M.W. 2007. Medieval Drought in the Upper Colorado River Basin. Geophysical Research Letters 34, L10705. Abstract: [http://onlinelibrary.wiley.com/doi/10.1029/2007GL029988/abstract] This is the peer-review scientific paper that the National Geographic article on the Colorado River is written about.

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