DryStoneGarden

Failed Moss Rock Wall

In light of all today’s talk about tearing down that (Berlin) wall, here’s some photos of the biggest wall to come down in my neighborhood this past winter, when a section of hillside pushed a moss rock retaining wall into the road. Must have been a shock to the homeowner and whoever built it (not me).

Though, without sounding like I’m piling on the unfortunate builder of the wall, it was predictable that this wall would fail. A three foot high wall is supposed to be two feet thick at the base, and this wall isn’t even one foot thick. It also doesn’t have a proper foundation or gravel backfill. I see a lot of failed retaining walls around town, and the common denominator is that they are always backfilled with dirt instead of the drain rock or rubble that virtually every book or manual recommends.

Failed Moss Rock Wall

Intact Section of Wall

The wall is still intact where the bottom course has bigger rocks and the rocks are toed in against the curb.

Failing Section of Wall

Failing Section of Wall

Moss Rock

Two more waller nightmares are below. (more…)

Pack Mules on Duck Pass Trail

The topic for this month’s design workshop at Gardening Gone Wild is dealing with slopes. The description mentions “tips for building steps and paths to make slopes easier to navigate,” so I thought I’d cite the source I learned from, the forest service Trail Construction and Maintenance Notebook, which is online and in the public domain (Who owns this government document? We do!). The text might have a few elements geared towards public trails rather than residential gardens, but the diagrams are good and the principles are solid.

Step Construction

‘Build stairways from the bottom up, at a break in the grade. The most common mistake is to start part way up a grade. If you do so, the trail will wash out below the stairs. The bottom stair should be constructed on a solid, excavated footing. If it is constructed on top of exposed rock, it should be well pinned to the footing. Each successive stair is placed atop [or against] the previous stair. Dry masonry rock stairs usually rely on the contact with the stair below and with the footing to provide stability.

‘Hikers, especially backpackers, generally don’t like steps and will walk alongside them if there is any opportunity. The steps need to be comfortable to climb or they won’t be used. This means keeping the rise a reasonable 6 to 8 in (150 to 200 mm) and the run long enough to hold a hiker’s entire foot rather than just their toe. It’s helpful to armor the sides of steps with rocks to encourage users to stay on the steps.’

Stepping Rock and Riser Stairways

‘The most important area of the step is usually in the run. This is where most traffic steps as it climbs. If the step is composed of something like a board on edge with fill behind it, then the traffic will step onto the landing. Almost all foot traffic descending the step will walk off the edge of the step. The top of the step (and landing) should be stable and provide secure footing. The edge of the step should be solid and durable. The face of each step should not contain a batter that creates a “face run” of over 2 in (50 mm) from top to bottom. This is particularly important as the rise of the step increases.

‘Steps with landings are a bit harder to secure in place because the stairs do not overlap. Each step can either be placed in an excavated footing and the material below the rise removed to form the landing of the next lower step. This is usually the most stable arrangement. Or the step can be secured on the surface and fill used to form a landing behind it. The material used to provide the rise does double duty as a retaining structure when the landing consists of tamped fill. These steps must be seated well to prevent them from being dislodged by traffic. For stock use, landings should be long enough to hold all four of the animal’s feet.’

Riprap Stairway

‘In more primitive settings, you don’t need a uniform flight of steps as long as the route is obvious and there is solid tread at each stepping point. In the Sierra, a cross between cobblestones and stairs, locally called riprap, is commonly used for this purpose.

‘If the stairway climbs straight up the hill, each step should be slightly crowned to drain water to the edges or slightly sloped to one side. When the trail traverses a slope, each step and landing should be slightly outsloped. Water should not be allowed to descend long lengths of a set of steps or to collect on or behind a step on the landing. A drain dip where the trail approaches the top of the steps is a good idea.

‘In all steps, the key is to use the largest material possible and to seat it as deeply as possible. Rocks should be massive and rectangular. On steps that traverse a slope, it helps to seat the upper end of the step material in footings excavated into the slope.’

Rock Staircase

Best practice for building a stairway these days, if the rocks are big enough, is to butt them against each other instead of on top of each other. That way it is possible to repair one of the steps without redoing the whole staircase.

Rock Staircase

It doesn’t say in the notebook, but I was taught to kick test every step. If the stone moves when you kick it, it isn’t solid enough. A bit of a shock, sometimes, to see someone kick the structure you just labored on, but the step is definitely going to get kicked when people use it, so you might as well find out if it is going to last. You want to feel confident that your stairs are safe. It’s scary enough the first time you see a mule train crank through a set of steps that you’ve built even when you know the steps are solid. There aren’t mules in residential backyards, but the foot of a 150 lb. person can easily impact with 300 lbs. of force, so the basic principle is the same. Steps should be strong.

Steps also need to be regular. The test is to walk up and down the stairway without looking down at your feet. If the rise and run are even, you shouldn’t trip or stumble.

Old Town Wall Steps

In the front country I usually don’t get to work with stones that are “massive and rectangular,” but I still kick test every step and walk the staircase with my eyes closed. This set of steps, built with a local sandstone called Old Town Wall, was a lot of work, getting the risers to all match and the stones all interlocked enough to stay in place. I was working for a designer who is a serious dry stone purist, so mortar was out of the question. I think the steps and cheekwall took me longer than the entire rest of the wall.

Mortared Arizona Flagstone Steps

When it’s up to me — though I’m a dry stacker at heart — I usually build steps with mortar, usually by stacking flagstone with a recessed mortar joint. I don’t think that method holds up in areas with heavy freezes and probably not if the steps are going to be used by mules, but it does well in Bay Area gardens. A before photo of these steps and another mule photo are below. (more…)

Tenaya Peak

I have a feeling it might be self-indulgent to post about rock climbing for a largely non-climbing audience — it has a distinct ‘Look at me, I’m on top of the rock!’ quality — but there is clearly some connection between my interests in stonework and rock climbing, so I’ll go for it. In any case, what Anita and I do is often not so much rock climbing as it is vertical hiking, long climbs that are not particularly difficult but very scenic. We recently managed to sneak in a trip to Tuolumne Meadows and the Tenaya Lake area to do some absolutely beautiful vertical hikes before the fall planting season swallows us up for a while (55 lbs. of bulbs coming, among other things). It doesn’t get much more scenic than the area around Tenaya Lake.

Tenaya Summit

Tenaya Peak was probably the highlight. The view from the top includes Half Dome and all of the peaks of the Tuolumne area, and the climbing is low-angle and easy. The approach morphs into the climb and eventually you think, ‘Maybe I should put on my Spiderman rock shoes,’ and then a while later you think, ‘Maybe we should rope up,’ and then later you realize, ‘ Wow, I’m on the top, what a view.’ Rubberneckers in the parking lot and other non-climbers never believe me, but all that’s needed is a pair of sticky-rubber shoes with someone to manage the rope and anyone could do this climb. It’s truly beautiful.

Tenaya Lake

Foxtail Pine on Tenaya Peak

There’s always a surprising number of plants growing on the rock. We got to to hang out with one of the poster children for global warming, the pika. Pika’s can’t deal with heat and for the most part retreated up onto alpine peaks a long time ago. Now that the climate is warming even more, they are stranded on those peaks, unable to migrate north to cooler locations.

Pika!

Stately Pleasure Dome at Tenaya Lake

We climbed a few of the other domes in the area. The Stately Pleasure Dome is appropriately, if a bit grandiosely, named. Great White Book, up the white dihedral near the center of the main face, is one of the most enjoyable climbs I’ve ever done. Pywiack Dome is another dome we climbed, an almost unbroken slab. It’s all some of the most perfect granite I’ve ever seen.

Pywiack Dome

Can you spot the climbers?

Looking around on wikimedia, I found some photos that zoom in on climbers on the dome. You can click to enlarge.

Can you spot the climbers?

Climbers on Pywiack Dome

That’s not us, but we did rappel from those same anchors.

Glacial Erratics at Lake Tenaya, by Edward Muybridge c. 1870

I also found this copy of an old stereoscope from the 1870’s. That man clearly wishes he had my sticky-rubber shoes to climb that boulder with.

Look at me, I'm on top of the rock!

——–

Yosemite National Park, especially the Tuolumne Meadows and Tenaya area, is my favorite place in the Sierras. Pam at Digging is of the same mind, with a post calling Yosemite the most beautiful place on earth. She’s writing about national parks this week and compiling a list of posts from other bloggers. Check here to see the ongoing collection.

Devil's Postpile National Monument

Probably the most striking geological feature on the eastside, an area full of geological features, is the Devil’s Postpile, one of the world’s best examples of columnar basalt. Columnar basalt is one of those natural elements that looks unnaturally geometric. It forms when it lava cools very, very slowly and evenly. The lava starts to contract and then crack, and because it cools so evenly the cracks form into hexagons, the most stable and efficient shape. As the Park Service page about the formation of the Postpile explains, “a hexagonal system provides the greatest relief with the fewest cracks.” (Bees use the same hexagonal system in their honeycombs because it forms a matrix with the largest amount of storage space for the least amount of wall.) Devil’s Postpile isn’t the only place where this has happened — the Wikipedia entry has links to many other columnar basalt cliffs, and pieces of columnar basalt regularly show up at stoneyards in the Bay Area –but the columns at the Devil’s Postpile are especially long and regular.

The Devil's Talus

The base of the cliff has the world’s coolest talus in my opinion. My crew was so well trained/indoctrinated that their first comment was how great these pieces would be for building steps. The park service doesn’t even let you climb on the talus, though, let alone build with it.

The Devil's Patio

Possibly the best part is that a glaciar carved off the top and made a natural patio.

The Devil's Paver Pattern

It’s uncanny how much they look like rough-cut natural stone pavers. Hexagons are stable because three joints come together at every vertex, making for a nice oblique 120 degree angle. The park service says that at Devil’s Postpile 55% of the pieces have 6 sides, 37% have 5, 5% have 7, and the remaining 3% have 4 sides or fewer. That’s a high percentage of hexagons compared to other sites in the world.

The Devil's Grading

The grading is a bit extreme on parts of the patio.

Surprisingly Comfortable

Ahhh, nice, soft basalt. My crew never saw a flat surface that couldn’t be slept on.

(more…)

Rock Step 'Clancy'

Instead of a bridge, my crew spent most of our time building rock steps, primarily on Duck Pass Trail in the Mammoth Lakes basin.

Arrowhead Lake

The trail to Duck Pass is one of the area’s quickest routes up into the high country, so it gets a ton of usage. The first section is a series of steep dusty switchbacks through lodgepole pine forest, but then you’re up in granite country the rest of the way to the pass. Arrowhead Lake is only a mile and a half in, with a fifteen foot high rock to jump from (unbelievably refreshing after a day of moving rock, jump at your own discretion), and then Skelton Lake’s another mile and Barney Lake’s another mile after that.

For some reason, this trail somehow became THE TRAIL for cross-country running teams from Los Angeles. Every day, we would have entire high school and college teams run through our work site, forty or fifty runners at a time, once on their way up and then again on their way back down an hour or two later. I’d never worked on such a popular trail. It was frustrating to have people constantly walking through our work site, but then, on the other hand, I’ve never had so many people thank me for anything I was doing. Literally hundreds of people thanked us. A much used and much loved trail.

High Timber Step

The trail is slowly evolving into a giant staircase. Because it’s a steep trail, gullies form and then steps are installed to try and control the gullies. The steps hold the tread in place on their uphill side, but then the downhill side of each step slowly erodes and it becomes necessary to add another step in front of it, which inevitably needs another step in front it, and so on. My crew spent the bulk of our time building new steps in front of the steps that past crews had built, and future crews will no doubt build more steps in front of ours. At times it felt a bit sisyphean.

Rock Step 'Bigeasy'

The steps we built are western trail steps, designed for horses and mules. Each step is supposed to be 4-6 feet long so that a horse can have its front and back legs on each step before stepping onto the next one. This step, Bigeasy, we actually sited even further in front of the timber step above it because that step is overly close to the next step above it. When that timber step inevitably rots out and needs to be replaced, it can be relocated a couple of feet forward and then all three steps will have proper spacing.

'Bigeasy' in transit

Finding the rock, aka rock-shopping, is probably the most enjoyable part. Moving it to the work site is often the biggest chore. Did I mention Sisyphus?

Rockbar Power Activate!

You do develop a good sense for the shape and size of each rock as you roll or skid it through the landscape, though. We gave names to most of the big ones. Basically, if you found the rock and spent enough time wrestling with it, if it was big enough and gravity-enfused enough, then it became ‘your’ rock and you got to choose a name for it. Names were usually descriptive, but sometimes random. For instance, Clancy (a big one fit snugly between Elton and John) was named after a forest service guy who had his macho turned up to eleven. Mammoth was an early 500 pounder. Bigeasy was surprisingly painless and easy to move. P.I.T.A. (Pain-in-the-Ass) was the opposite. Melon was low-hanging-fruit. Quickie was finished quickly. The macho, male names of our early rocks led to a series of less macho names, Howard and Jeffrey, then Fabio (very handsome), then Buttercup, Jewel, and Pearl. Showtime, the Three Musketeers, Mastodon, Alligator, and Shitzy round out the list, the last of the names I remember. A few of those steps and the view from near the top of Duck Pass are below. (more…)

Entrance to the de Young Museum

“Every time I hit a stone, it’s like my heart’s a little bit in my mouth.” Andy Goldsworthy

This Andy Goldsworthy installation, “Drawn Stone,” at the de Young is from 2005, but I didn’t have a blog back then and I’m generally slack about going to museums, so it’s just now that I’m checking it out and posting about it. Goldsworthy’s stone installations are always interesting to me, the way he often manages to (knowingly) break the rules about stonework while still remaining very attentive to and respectful of the craft. For instance, with “Drawn Stone,” the entire focus of the installation is a crack that runs through the sandstone pavers and slabs of the museum’s entrance. Installing a cracked paver is considered poor form, but he’s reveling in it, making it the entire focus of the installation. And in fact, it must have taken a lot of extra effort to crack the pavers and then match them up, so he even earns bonus points for doing something that would normally be frowned upon. Pretty bold.

The installation was originally named “Faultline,” but Goldsworthy changed the name along the way. I don’t know anything about the reasons for the change, but it seems like he somehow found out that Californians don’t really like earthquake-themed art, and so he decided to keep that aspect more low-key, the way Californians like it. In this case, it’s totally appropriate to have an earthquake theme — the new de Young was actually built because an earthquake made the old building unsafe — but it’s more in keeping with the local aesthetic to keep that aspect out of the title. And the piece is overall fairly subtle, anyways; several people didn’t notice it until I took out my camera and started snapping photos.

Goldsworthy is always an interesting talker, and KQED’s website has a 2005 segment about the installation with him talking about learning to break pavers (the best way is to just whack them with a hammer) and other aspects of the piece. The museum website has his artist’s statement along with a photo of him on top of one of the slabs, holding a sledgehammer, with the wedges and feathers still in the slab. It’s a fair bit of work to split a slab that big, but it must have been satisfying. Photos of cracked pavers and slabs are below. (more…)