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Dry Stack Walls: A Pioneer Legacy, Part Four

Part Four: Terrace Walls

The third article on Dry Stack Walls provided photos and interpretive text on the identification and construction of walls that can be found at mines and settlements; including heavy walls for mining operations, corrals, retaining walls and foundations. Part Four describes walls built for the purpose of constructing terraces for housing and cemeteries.

Previous articles have focused on dry stack walls that were primarily built for transportation, mining activity and corrals. We now turn to walls that served a much more personal need – the construction of terraces for housing and for cemeteries. The fundamental purpose of a terrace is to provide a flat area in terrain that is not naturally level. I submit that there are no naturally occurring flat areas in the mountainous mining districts of Arizona.

Terrace Wall
Figure 1, Terrace Wall for Buildings

The criteria I use to classify a terrace are based on two simple, but essential, points: First, there must be an upper retaining wall (whether natural or man-made). Second, a lower wall must also be present. The area between these upper and lower structures is (or was at some past time) essentially ‘manufactured’ flat ground. Figure 1 provides a clear example of a terrace. In this case, the upper wall was cut into the rocky hillside and the lower dry stack wall was constructed using shaped stone. It should be evident that the terrace area was created by providing additional fill soil. This terrace provided space for two houses, as evidenced by the remains of the wood structures in the center of the photo.

Typical Dry Stack Terrace Walls
Figure 2, Typical Dry Stack Terrace Walls

Figure 2 is possibly the best illustration I have found of a terrace wall structure that provided a ‘nearly perfect’ flat area. The combined height of both walls is nearly five feet (from the bottom of the lower wall to the top of the upper wall). Sedimentation at this site has been effectively eliminated for more than one hundred years, even though the two walls were constructed using irregular (unshaped) native stones. As in Figure 1, fill soil was used to create the flat terrace.

In case you haven’t already noticed, the two walls in Figure 2 and the lower wall in Figure 1 rise a few inches above the level of the soil. Why is this? Take another look at the uphill side of the terrace in Figure 1, where two things become obvious: (1) Steep hillsides, and (2) very thin topsoil. In fact the term ‘topsoil’ is, practically speaking, a euphemism. Persistent exfoliation of granitic rocks in the mountainous areas produces a loose, sandy material that is easily washed downhill by seasonal rains where, ultimately, it is deposited in the creeks, washes and gulches. Consequently, the ‘soil’ that you find on the steep hillsides is exceedingly thin and loose. The essential point is that these terrace walls were not only constructed to provide flat areas at a point in historical time, but to also guard against future erosion and sedimentation from the uphill slopes.

Terrace Wall
Figure 3, Terrace Wall Covered by Foliage

Figure 3 shows a terrace wall that is only visible from a close distance. Two search methods can be used to infer the location of walls of this type. First, the terrace above this wall can only be observed from a distance and at a higher elevation. I found this wall by scanning the terrain from several hundred yards from the west and about three hundred feet above. The terraced area was ‘flat’ and relatively free of vegetation – a definitive indicator of past pioneer activity. Second, notice the line of mesquite and acacia trees that are located on the margin of the wall. These trees have prospered from the soil used to create the terrace. I believe they have also benefited from the reduced rate of runoff (that is, an improved rate of moisture absorption). Whenever you observe a straight line of vegetation in a remote area, you can be reasonably certain that human activity was involved. Naturally straight lines are exceedingly rare!

Cemetery Terrace Wall
Figure 4, Cemetery Terrace Wall

Figure 4 shows a short section of terrace wall at a large pioneer cemetery. Close observation of the general slope (from left to right) shows a steady downward incline and it is doubtful there was any intent to create ‘flat’ ground in the upper portion of the cemetery. Instead, this dry stack was probably intended to mitigate erosion. There are two additional terrace walls to the right of this photo that rendered more level ground for graves. This wall faces just a few degrees north of west, so it is exposed to considerable sun light. Notice that these westward-facing rocks have been ‘bleached’ by a century of exposure.

Cemetery Wall and Wood Post
Figure 5, Cemetery Wall and Wood Post

Figure 5 shows the corner of another dry stack cemetery wall. In my experience, at least, I have found very few derelict cemeteries that still have wood posts or other structures (such as grave markers). In this example you can see a post at the upper right that served as part of a fence along the southern margin of the cemetery. The wall in this photo appears to lean into the steep hillside, but it has not been effective in preventing sedimentation. The area between this and a lower terrace wall has seen the deposition of several inches of soil over the decades.

It is usually a straightforward matter to infer the original purpose of a dry stack wall, as the photos in previous articles will attest. Figure 6 shows one of the terrace walls at the site known as the ‘Arrastre Cemetery.’ Although the upper and lower areas now contain twenty-two graves, the walls were actually constructed to provide work and (probably) living space at a Mexican arrastre; located out of view to the right. Historical accounts indicate the arrastre could have been in use by the middle 1880’s, but was abandoned near the end of 1890. The two terrace areas were subsequently used for burials and the arrastre was partially dismantled to provide headstones at some of the graves. The site was cleared of undergrowth and dead tree limbs during a series of restoration projects in 2008. Otherwise, this wall would be barely visible – even from distance shown here.

Terrace Wall
Figure 6, Terrace Wall at Arrastre Cemetery

This dry stack gives the appearance of having been crudely built, and that is indeed true. Arrastres were known as ‘the poor man’s mill’ and were primarily used to ‘prove’ the value of an ore vein. This wall lacks the craftsmanship and aesthetic qualities evidenced in other walls; possibly because there was no objective beyond the immediate extraction and amalgamation of ore. While the size and weight of these stones have kept the wall in place, the irregular shape of the rocks has allowed sediment to flow over and through the wall in the time since it was constructed.

Notice the surface in the foreground of the photo. It has a reddish cast and is relatively dark. Seasonal rains have steadily washed soil from the hillside onto the terraces. More than a century of undisturbed plant growth has been deposited on the site and mixed into the soil by animals. The ground slope between the upper and lower walls only became apparent after the lower terrace was cleared of undergrowth and debris. In fact, the actual base of the wall is more than twelve inches below the visible surface and there are at least two more courses of rocks. This photo is an example of why careful observation is important. If you believe you have located a terrace (that is, with upper and lower dry stack walls), remember that the purpose was to create a flat area. If you observe a sloping surface, that is an indicator of sedimentation.

It can be challenging and, at times, frustrating to separate what you see ‘today’ from what a site would have looked like more than a century ago. Be patient and do not let your first impression drive your understanding of a pioneer site. There is always more than meets the eye!

What Do These Photos Tell You?

  1. Good craftsmanship and thoughtful placement of dry stack walls can produce terraced spaces that will prevent erosion and sedimentation.
  2. Low terrace walls are easily masked by plant growth and can be very difficult to locate, particularly if they are above your line of sight. However,
  3. If you can gain advantage with elevation, the flat area behind a terrace wall will be more easily revealed.
  4. Look for other indicators, such as straight lines of tree growth as an aid to locating dry stack terraces.
  5. Sedimentation from slopes and soil deposition from flash flooding may mask the height of many walls.

In Part Five, the final article of this series, we will examine dry stack rock cabins that are found in the mining districts and settlements of pioneer Arizona.

Last 5 posts by Allan Hall

2 comments to Dry Stack Walls: A Pioneer Legacy, Part Four

  • Brad Johnson

    What should be used as a foundation, and what depth, for a short dry-stack retaining wall?

  • Allan

    Dry stack walls are, by definition, built without mortar and every example in these articles was constructed without a cement foundation. From what I could observe, the walls were generally not built below grade, except in cases where there was an intent to level a slope. Most of the heavy walls (not cabins) followed the contour of the terrain.

    Two observations that may be useful:

    1) Heavy load walls (such as mine dumps, mill sites and roads) were usually of uniform thickness. That is, the top of the wall was about the same thickness as the base.

    2) The rocks used in these walls were rough and angular in shape. This type of rock provided better interlocking resistance that smoother river rock could not.

    There are a number of web sites that provide tutorials on dry stack construction that should be helpful. Use the search term “dry stack wall construction” on Google or with other search engines.

    Thanks for reading the article.