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Lockwood has come up with a sexy topic for this month's Accretionary Wedge — yes, you guessed it (or already knew): Sexy Geology. For the record, Lockwood has defined "sexy" as:

I mean geology that makes your heart race, your pupils dilate. Rocks and exposures that make you feel woozy and warm. Structures and concepts that make your skin alternately sweaty and covered with goosebumps. Places you've visited, read about, or seen photos of that make you feel weak-kneed, and induce a pit in your stomach.

I'm in a bit of a rush these days it seems, and so I'm just going to post a couple photos of some geology that always turns me on, and two links to related posts from earlier this year.
Beds and bedding are always of interest to geologists; cross-bedding is best.

Related Posts:
Cross-Bedded
More Cross Bedding

Also see Callan's recent post.
Photos are of the Jurassic Navajo Sandstone in Zion National Park, on Utah route 9, the Zion–Mount Carmel Highway, a few miles east of the Canyon Overlook Trailhead.

UPDATE: Accretionary Wedge #37, Sexy Geology, is now up at Outside the Interzone!

After coming out of of "the cathedrals" at Cathedral Gorge, MOH and I went on a little hike.
The trail goes north up the gorge, from the CCC Picnic area (facilities and water tower built by the CCC in the 1930s) to Millers Point, a one way distance of about a mile (MSRMaps location).
Fascincating textures can be seen in the Pliocene Panaca Formation along the way. Here, differential erosion of harder, thin sandstone layers interbedded with softer mudstone layers have created interesting mini-columns and maybe even some little mini-cathedrals hidden in the shadows.
My hand is straddling two sandy layers and a mudstone layer sandwiched in between. A curious jigsaw-like texture has developed over the mudstone. Essentially these are tiny gullies or rills created by water running down the outcrop.
We've now made it into the beginning of the steep, northern end of the trail, and I've turned around to look southward down the gorge.
Steep: The northern part of the trail is steep, especially in this section of hand-built stairs held up by partially eroding railroad ties. Beyond these wooden steps are metal stairs that go from ledge to ledge over the steepest sections of the trail.
Instead of hiking the stairs all the way to Millers Point, we stopped on one of the middle ledges. Columns capped by sandstone can be seen from several vantage points along this northern stretch of the trail. The scale of these hoodoo-like features is difficult to appreciate: they are often smaller than similar erosional features at Cedar Breaks, for example. These are maybe two hundred feet high at most.
This is one of several holes eroding into the broad ledge we were standing on. I peered in, but couldn't lean out far enough to see anything, so tried holding the camera out as far as possible, having it do the peering for me.
I wondered if this hole could be the top of one of the cathedral-like columns we had seen from below while wandering around near the picnic area (first post).
An overexposed photo showed me that this hole only goes down a few feet (railroad ties for scale).
Some of the other "holes" and irregular erosional features near the edge of the ledge may indeed go downward to become cathedral-like inner columns, but I really didn't want to check them out too closely!
Now I've jumped two or three hundred feet upward and two or three years back in time to show this photo taken from Millers Point. The broad ledge we were on is below; the stairs to the right along with a smaller set of stairs down on the ledge (barely visible on the far left part of the ledge) give some sense of scale to the columns and gorge, and to the broad plain into which the gorge has been eroded. The bentonitic, tuffaceous clays, silts, and sands of the Panaca Formation — essentially water-laid tuffs, diatomaceous in places — were deposited in a closed, Pliocene-aged basin. The source of the tuffaceous material is reportedly the Caliente caldera complex south of Caliente, NV — way off in the distance on the far right — which was active in latest Oligocene to middle Miocene time, from about 24 to 13 Ma.

The Panaca Formation reminds me somewhat of the Triassic Chinle Formation, a partly bentonitic formation seen on the Colorado Plateau at the Painted Desert. Possibly the Panaca will look like the Chinle in the far future, if it has the good fortune to be preserved, rather than being eroded as it is now, southward into Meadow Valley Wash, from there southward into the Muddy River (formerly into the Virgin River), and from there into the Colorado. We are outside the Great Basin!
We finally headed back toward the CCC picnic area, just beyond that final rise of sand highlighted by the early afternoon sun.
Gratuitous sand photo. And darn! I forgot to collect any!

Some References:
Rowley, P.D., Nealey, L.D., Unruh, D.M., Snee, L.W., Mehnert, H.H., Anderson, R.E., and Gromme, C.S., 1995, Stratigraphy of Miocene ash-flow tuffs in and near the Caliente caldera complex, southeastern Nevada and southwestern Utah: in Scott, R.B. and Swadley, WC, eds., Geologic Studies in the Basin and Range - Colorado Plateau transition in southeastern Nevada, southwestern Utah, and northwestern Arizona, 1992, U.S. Geological Survey Bulletin, 2056-B, p. 43-88.

Rowley, P.D., Snee, L.W., Mehnert, H.H., Anderson, R.E., Axen, G.J., Burke, K.J., Simonds, F.W., Shroba, R.R., and Olmore, S.D., 1992, Structural setting of the Chief mining district, eastern Chief Range, Lincoln County, Nevada, in Thorman, C.H., ed., Application of structural geology to mineral and energy resources of the central and western United States: U.S. Geological Survey Bulletin 2012, p. H1-H17.

Nevada-Utah series so far (in trip-time order):
Cathedral Gorge I
Cathedral Gorge II: The Hike (this post)
May Utah Trip to be Continued
Cross-Bedded
More Cross Bedding
Bighorns on the Overlook Trail

There we were, at the end of the Canyon Overlook Trail in Zion National Park, looking west toward the southern end of Zion Canyon, where the North Fork of the Virgin River flows through (not that you will see it the Virgin in this post).
Reddish brown to orange cross beds of the Jurassic Navajo Sandstone (Jn) were everywhere, available for angled sun bathing, photography, and a bit of careful climbing. And beyond and above, there is the ever-present white (and still cross-bedded) upper portion of the Navajo.
I zoomed in on a fascinating section of white to yellowish sandstone in the cliff below the upper white sandstone: cross beds amongst cross beds.
A small tree, and a mini-tree below it, grow near the edge of the 400-foot drop into the lower canyon of Pine Creek. Wedge and trough cross strata can be seen in the nearby reddish cliff behind the tree. In the distance, an inset arch may eventually form beneath the uppermost reddish layer, below the upper white sandstone.
I looked over the edge at the actual trail end, which has a convenient metal railing. One of the windows for the mile-long tunnel on the Zion – Mount Carmel Highway (Utah S.R. 9) can barely be seen in the deep shadow to the right of the sunlit cliff.
If we could hang way over the edge, we'd see The Great Arch, an inset arch just beneath us. I took the photo from one of S.R. 9's many switchbacks (six, to be exact) as it makes it's way up to the west tunnel entrance. This kind of inset arch is sometimes called a blind arch.
Finally, we have to turn away from the overlook to head back towards the trailhead and the road east.
A narrow part of the trail, with a small dropoff, heads back toward the cave seen in the last post. The inset arch visible from the cave, across the slot-canyon portion of Pine Creek, can be seen in the shaded background of this photo.
Around the corner, the trail goes into a sandy narrows between pale orange sandstone and a reddish brown layer. The cross beds here (and in much of Zion) are generally dipping to the south, as can be seen in the far cliffs, indicating that the wind blowing the dune sand came from the north. Here, the the pale orange beds we've been walking on are dipping to the south, and the reddish brown layer we're about to walk on dips to the north.
On the way back, the Bighorn Sheep we passed on our way out had moved closer to the trail (right on the trail!) and closer to the trailhead. This one was munching on bushes near this magnificent exposuring of cross bedding. I'll show more pictures of these critters in another post.
We're now in the home stretch on our way to the parking area, having passed the overhung cave. This is one of the heavily hand-railed sections of the trail: there's a ledge about 5 feet below the trail, then a couple-hudred-foot drop to the slotted canyon of Pine Creek below. Ahead, the trail goes around a corner to turn more easterly, goes past the leaning tree of the first post, and then goes into relatively steep, somewhat slippery, sand-covered sandstone ledges and the doubly railed steep stairs carved in sandstone at the beginning of the trail.

I strongly recommend going out of your way to take this hike.

This mini-series will now go in at least two directions, one being the road from St. George, Utah, to Zion, through the tunnel and over the pass to Mount Carmel Junction, with a couple photos on the loop road toward Cedar Breaks and into Cedar City. There will be no pictures from Cedar Breaks: the highway department hadn't even considered plowing snow from the south entrance, where it was at least two feet deep.

I didn't know we were going in search of cross bedding the day we decided to circumvent downtown Zion Canyon (a place you can get to via shuttle, a Red Pass, by bicycle, or on foot), to take the side road under and over the mountain: the Zion–Mount Carmel Highway. I remembered from long ago, and indeed the Zion Canyon Map confirmed, that an overlook trail takes off back towards the canyon just past the main tunnel, a tunnel that is 1.1 miles long and was built in 1930 (Google Maps Street View of the tunnel near the first window). I had very little memory of the trail, other than that it provided an overlook of the lower part of Zion Canyon.

The trail is entirely in (or on) the Jurassic Navajo Sandstone, a thick dune sand recognizable in cliffs from miles away. I smiled the entire length of the trail and back: I think it was the cross-bedding. The hike may have stirred some sentimental sentiments (about these cross-bedded sediments), but if so, the stirred memories are buried too deep to make a difference to me today.

The trail is a 1 mile round trip with a total change in elevation of 163 feet. It's rated as moderate, mostly because of some narrow passageways and long drop-offs. Handrails are provided in particularly steep parts and where drop-offs are particularly dangerous or where the trail is narrow or slippery. At least one person has died after falling 400 feet from the end-of-trail overlook.
The trail begins in a set of steep stairs carved into a pale orange part of the Navajo.
Views are everywhere stunning. A leaning tree frames the fore trail.
Looking back under the leaning tree provides a view of the ever-present cross bedding.
A somewhat narrow part of the trail has a small seep near the base of a sandstone cliff.
Cross bedding! The trail, hidden by trees at the base of the cliff, goes on beyond a little embayment in the canyon.
More cross bedding, a little below the previous shot. Rocks are perched in a manganese-stained gully.
The trail — becoming a boardwalk hung over a hundred to two hundred feet of air — is about to enter a small alcove or cave.
Water seeps all along the base of the overhang, drips down the back wall, and drips from the ceiling. The air was already cool before we entered the cave, possibly not quite 70° F; inside the cave it was cooler and damper, probably a great place to hang out in the heat of summer. For scale, you can see footprints in the foreground on the sandy floor; the height near the farthest shade-sun boundary (with tree to the left and rocks to the right) is about 12 feet.
An inset arch can be seen from the cave, across a slot-canyon portion of Pine Creek.
The trail is still hidden by trees.
Now we're walking along a narrow ledge cut in sandstone, just above this Indian paintbrush.
Looking back toward the trailhead and the bridge coming out of the mile-long tunnel, we can see the slot-canyon portion of Pine Creek. MOH said he could see the bottom of the canyon with binocs. The rocks on the bare sandstone in the lower part of this photo are the same rocks perched on cross beds from six shots back (second of two cross bedding photos before the cave).
The rocks will someday plunge into the slot canyon below.
While taking a little side trail, we came upon a small herd of six to ten Bighorn Sheep, ewes with at least two lambs.
A lamb amongst the cross beds.
After a little less than an hour of moseying along, we arrived at our destination, the canyon overlook above The Great Arch (MSRMaps location, Google Maps photo).

NOTE: This post is part of a slow-to-develop geoblogospheric meme: Sentimental Sediments, started bravely by Dana over at En Tequila Es Verdad. Entries are supposed to be about your favorite sedimentary rock or sedimentary structure. As a hard rocker, I had a hard time thinking of any particular sed rock I'm actually sentimental about, but the whole of red rock and canyon country in the southwest contains my favorite sedimentary rocks and favorite stratigraphy, with any sentimentality on my part dating back to 1971 or 1973. At first I didn't think I had any digital photos from the area, but I have some from Fisher Towers and the San Rafael Swell. Now I also have some from Zion. :)

The entire geoblogosphere has been tagged!

Some References:
Loope, D.B., and C.M. Rowe, 2005, Seasonal Patterns of wind and rain recorded by the Navajo Sandstone: Canyon Legacy, vol. 54, p. 8-12.

Loope, D., L. Eisenberg, and E. Waiss, 2004, Navajo sand sea of near-equatorial Pangea: Tropical westerlies, slumps, and giant stromatolites, in E.P. Nelson and E.A. Erslev, eds., Field Trips in the Southern Rocky Mountains, USA: Geological Society of America Field Guide 5, p. 1-13.

Loope, D.B., M.B. Steiner, C.M. Rowe, and N. Lancaster, 2004, Tropical westerlies over Pangean sand seas: Sedimentology, vol. 51, p. 315-322.

Stewart, Michael, 2006, Zion National Park: University of Illinois, Geology 104, Geology of National Parks and Monuments, Course Lecture Material (web only).