The Nature Conservancy 3-Links Tour, April 2005

 

On April 24, 2005, Ralph Waldt, the Naturalist for TNC 3-Links Ranch, led a Nature Walk along a portion of the stretch of San Pedro River which TNC is now working to restore. Below, Ralph introduces the subject to a group of ecotourists near the riverbank (Click on the image for a close-up of Ralph):

The group rested at several points along the river. Note the gallery forest cottonwoods, common throughout the area. This forest, characterized by a Fremont Cottonwood-and-Gooding Willow association, is unique among North American forests. According to Ralph, about 4 1/2 miles of perennial water now flows through the 3-Links lands, and considerably more may emerge depending on drought conditions. The San Pedro River is the last free-flowing river in the entire desert Southwest.

At one point in our walk, Ralph picked up some lengths of bark-stripped logs lying along the riverbank and observed that the San Pedro has again become a "beaver river". (See Beavers along the San Pedro.) The two images below left and center show the teethmarks made by a beaver in cutting the tree, while the one on the right shows those made when one consumed the bark. (Click on each image to enlarge it)

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According to Ralph, this beaver moved in from upstream (where a beaver population has been recovering for some time), and was in the area during 2004, but was presumably washed downstream with the seasonal flooding of the River sometime last year. More will probably appear here from time to time (though so long as the river's periodic massive flooding pattern continues, their stays may be temporary).

At another point, people were discussing plants, birds, and other fauna seen along the streamway. Note the dark clay strip running horizontally along the lower portion of the cut-bank behind them: (Click on the image for a close-up detail of the dark clay.)

Ralph suggests that these dark clay layers, which appear along the river at a number of points here, mark the presence of prehistoric swamps, or in some locations Cienegas, known to have been distributed along the River in this area prior to the 1890s, when the River began the downcutting which has led to today's typically fairly deep entrenchment. In the photo above, the dark deposits marking older swamplands are overlain by several feet of subsequent deposition prior to the entrenchment. As the group continued its tour upstream, we came upon other patterns of clay layering, as shown below:

Here the swampy deposits have a depth of fifteen feet or more, and continue right to the topmost layer, indicating that a swamp (or cienega) must have been present here immediately prior to the 1890s entrenchment, and must have existed here for hundreds, perhaps thousands of years before.

A short distance upstream, we saw below -- in a clay layer some 15 feet below the top of the old floodplain -- collections of fossil freshwater molluscs eroding out of the deposits: (click on each image to enlarge it)

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In the images just above, at left the fossils are barely evident from a distance, but closeup a considerable variety of shells may be seen, and at right some have weathered out and now lie under the water in today's streambed, where they will eventually be deposited further downstream in a second sedimentary formation.

Further upstream, we encountered stands of Coyote Willow (Salix exigua Nutt.), a kind of willow tree infrequently seen in our area but an important riparian stabilizer, which is now spreading along the River at this point. In the image below, it is the relatively pale green, low and densely packed cluster at left center, in front of the towering lone cottonwood:

Coyote Willow pioneers flood deposits along a river's edge, and forms dense thickets which both retard erosion and provide both food and habitat for wildlife. It is a favored food for Beavers, and a critically important habitat for the Willow Flycatcher, an endangered bird species in our area. Below is a closeup of the foliage:

Another riparian plant which is rare in our area but found along the San Pedro River at 3-Links is the BurrReed Sedge (Carex sparganioides sp.), shown below: (Click on the image for a close-up)

Members of the Sedge Family (Cyperaceae) resemble grasses and rushes, to which they are remotely related within the Order Poales (monocotyledonous flowering plants). They generally grow in wet locations. The inconspicuous flowers of the Burr Reed Sedge may be seen in the close-up image above.

We encountered numerous Monkey Flowers (Mimulus spp) blooming alongside the river: (click on each image to enlarge it)

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We also saw numerous birds along our route, including Gray Hawks, and managed to obtain distant images of the following: (click on each image to enlarge it)

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We walked much of the way in the river, especially where the banks are very densely vegetated, as shown below. Octogenarian John Wires, at right, leads the way in this photo.