Kelsey Canyon to Sierra Blanca Canyon Wash: a Recipe for Disaster
The Kelsey Canyon Corridor: Floodplain Challenges
Kelsey Canyon does not appear large where it crosses the Cascabel Road, but it drains part of the large grassland area called the Allen Flats, located beyond the Galiuros Western Range, at right on the map below:
As can be seen on the map above, it has cut a deep and narrow canyon through the Teran-Kelsey Escarpment after draining the extensive Allen Flats (far right), and in flood it can carry very massive loads of rock as well as water.
Many washes that cross the Cascabel Road in this area present serious danger to traffic during and after rainstorms. Below, after a storm in late July 2005, Kelsey Wash runs modestly.
In this example, careful examination indicated the Wash was safe to cross for the high-centered, 4wd vehicle parked here. However, the Kelsey Wash is notorious for carrying down substantial boulders when it runs more strongly than this, and becomes too dangerous to cross even at moderate depth. Usually the strong pulses are fairly brief, but from the perspective of long-term Cascabel residents they are also legendary. For a note alluding to the likely old-historical significance of this aspect of Kelsey Wash, see this side-page:
If Alternative "K" opted for a roadway crossing the Kelsey wash here, it would not only have to be several times as wide as that shown here, it would also have to be built with sufficient elevation clearance and structural integrity to bridge the occasional but sometimes Lahar-like rock-and-water debris flows that rush through here. A system of massive pillars or something similar would be required. (And if the roadway sought to ride the uplands further east across the wash, another and considerably longer version of the "Grand Bridge" type would be required.)
The Teran Wash Corridor
Proceeding further north, the very broad (and, further upstream, multiply dissected) Teran Wash strikes into the river at Milepost 20.
Once again, note the severe restrictions for location of either of the two Alternatives "D" and "K" here. Some massive enlargement of Cascabel Road would seem to be the only realistic possibility here, though again one should not discount the possibility of serious planner-envisioned upland routing. And the Teran Wash is a large one: note how the inflowing wash has cut out the high cliffs evident at the lower-left (southwestern) bank of the San Pedro here (for a photo image of part of this cliff-face, see further below).
Teran Wash drains a large basin lying eastward and southeastward from milepost 20. The extensive, high-angled Teran-Kelsey Escarpment bounds this basin on the southeast side, as shown below::
Like the other portions of the West Range of the Galiuro Mountains bounding the San Pedro River in this area, the Teran-Kelsey Escarpment shows strong block-fault tilting away from the River Valley. For more detailed views of this piece of the Galiuros, see this link: Teran-Kelsey Escarpment, and for geological context see Basin-Range Faulting.
The Teran Wash Watershed
"X" marks the spot where the wash crosses the Cascabel Road. Note the broad expanse of the Teran Basin at right-central in the map above. Teran Wash receives not only waters from the Teran-Kelsey Escarpment but even more extensively from the Red Peaks complex further to the north (both of these ranges are part of the Western Range of the Galiuro Mountains). And the map just above does not really even hint at what would be involved in building across the upland part of this wash (i.e., across that portion shown with the 4-wheel-drive roadway indicated, beginning a very short distance upstream from Cascabel Road. Moving upsteam, wash-roaders rapidly encounter multiple dendritic side-washes, each one tending steeper upstream than the last. For some minor hints of the situation, see this
Teran Corridor, Flood-plain route (the really likely Planners' Prospect?)
Long-term resident Barbara Clark has old maps of the Teran Wash confluence from early in the 20th century, showing that Teran Wash apparently entered the River at the grade of the bosque at that time, so -- as can be seen direcly below -- this marks a very considerable recent change, a drop of about 40 feet from near the current roadway to the floodplain.
This image of the Teran Wash road crossing below shows Teran Wash in very modest flow in late July 2005, with some of the vehicles waiting for the flood to subside while a higher-centered vehicle begins a run across. The problem in this instance was not rate of flow but the deep undercutting of the embankment in the foreground; much of the flow is out of sight because the embankment has been sharply cut on this side. The depth of the wash below the main grade of the road here is on the order of 20 feet. Again, imagine a bridge three to four times as wide as the Cascabel Road shown here, and raised more than 20 feet high above the Teran Wash floodplain.
So any large highway built across Teran Wash at this point (lower left above) -- and this is the best point where such a highway could be constructed here along the floodplain (both downstream and up from here form steeper banks) would have to be a large one with a substantial bridge on the order of the "Grand Roadway" described previously, again shorter vertically but much broader horizontally.
Note the power pole visible at mid-left top in the above photo. Across Cascabel Road from this spot is a single-lane road turnoff leading to the Oasis Bird Sanctuary, the Deacon's Cathedral, the La Margarita community meeting center, and the Cascabel Clayworks. All of these communities, normally small in number but regularly hosting large gatherings, would be significantly disturbed by heavy-truck traffic "bypassing" their immediate neighborhoods at grade.
Along many parts of the River basin in our area, severe downcutting of the river's channel has occurred, a process which accelerated along the river during and after the 1890s drought (see discussion of this process in San Pedro Changes). For example, a difference from the early years of this century has been noticeable near the Teran Wash confluence, where one side of a downcut channel is shown below, in July of 2006:
The channel here is about 20 feet deep, with the old pre-20th century floodplain, with its mesquite bosque, at the top of the embankment. Below, a March 2007 view from the edge of the mesquite bosque looking down into the River at this point:
Note the precariously situated mesquite tree hanging over the river at left-center of the photo. Below, vivid evidence of the continuous loss of this bosque to riverbank erosion:
While downcutting during the twentieth century has lowered the water table at this point, some 6 miles further downstream perennial stream reappears in a number of places, and there the riverbed is not so channelized. Entrenchment is a prominent but not continuous feature of the River in our area. For a wide-ranging discussion of changes in the vegetation of this area, see Changing Sonoran Desert Vegetation.
Below, the river in moderate flood, August 2005:
Below, this satellite image from Google Earth looks from the southeast toward Hot Springs Canyon, with Teran Wash entering the picture at lower-right. Clearly, building a freeway across the uplands on the western side of the river would be a very serious and hugely expensive undertaking; building it on the uplands of the eastern side would require large bridges across at least six substantial washes. Following a route along the current Cascabel Road would not eliminate these requisites, but would in addition raise very serious problems of ensuring continuing local road access for residents. Building it in the floodplain would require a many-pillared bridgeway. (In this paragraph we disregard the considerable ecological consequences associated with any of these versions.)
The Northern Endpoint of a Ridge-hopping Alternative "D"
At some points along the River in this area, some geologic facies of the San Manuel Formation rise behind the bosque on the west side of the River, occasionally forming erosional flumes of striking beauty. Below, just upstream from the confluence of Paige Wash with the San Pedro, these remarkable gray sedimentary hills erode down to the river in many fingers. They are post Basin-Range, flanking-mountains-erosional formations of Quiburis age -- 7.5 to 5.5 Million Years old:
These rapidly-eroding "badlands" provide many a cleft/flume refuge for nesting birds of various kinds. Click on the above image for a close-up view of these visually striking "badlands", and note the bird guano visible in that image. Since they also decay rather precipitously right down to the river's edge, it would seem nearly impossible to build a roadway either along or atop them. See their position on the map below, where this "Paige Formation" facies can be seen ending in a pointy triangle whose apex juts toward the icon "Cascabel".
Note that so far in our discussion of Alternative "K" issues we have bypassed Sierra Blanca Canyon, shown flowing to the river from far upper-right in the map just above. While it's true that the roadway crossing of the wash here near Milepost 22 is not a very imposing landscape, this wash too is a large and dissecting structure throughout its length further upland. Minor bridging would do for Alternative "K" at the Cascabel road confluence, but upstream requirements would be quite another matter. See the accompanying side-link for all a transportation planner might care to learn about this very interesting and beautiful wash: