The area between these two curves is a measure of the amount of Colorado River water that's arriving in the gulf in this particular year in the past. So, if we can take this measure here and somehow convert it to a natural volume of water, we can compare our paleontological record to the historical records of flow that have been captured by the USGS and the US Bureau of Reclamation. To do this, we're actually using two methods. One of them we thought we were stuck with, the other one we got lucky.

The first one, we're using two bivalves from the mouth of the river that were collected in 1884 and 1888. These specimens are very important to our work and we found them at the Smithsonian. We can look at these specimens, we can analyze the isotopes and we will see the signature of the river in their isotopic profiles. What's also important is that the United States Government kept sporadic records back then of flow through Yuma, Arizona. So we know how much water was flowing into the Gulf of California for these particular years. And we've used that to translate this amount of isotopic variation into a volume of flow.

More recently, we got really lucky. In mid-1997, the Bureau of Reclamation decided to release water from the dams in anticipation of a particularly heavy snowfall in the winter of 97-98 because of the pending El Nino. So, they released a bit of water in September and October but then in January or February they really let the dams rip and they opened up the gates and we had just this major flow of fresh water roaring down the Colorado into Mexico. Of course, farmers and cities and so on don't plan on that type of short term basis, short enough as it is so, most of this water flows right on through into the ocean. It's the first bit of Colorado fresh water to actually reach the ocean in any significant quantity since the 1960's.

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