The guided tour of Boundary Dam...

on the Pend Oreille River at the US-Canadian border, a concrete arch-gravity dam constructed in 1967 for hydroelectric generation, was nothing short of excellent. A big thank you goes to the engineers from Seattle City Light that owns and operates the structure for a terrific exploration of the facility.

View due north, down river and into Canada from the top of the arch dam, 338 feet (103 m) above the water surface.

View of Boundary Dam from river level, with the six transformer stations on the right where high voltage power lines exit the underground powerhouse.

Service tunnel entrance to the subterranean powerhouse, including the generator hall, transformer stations, the control room for operation of the structure and administrative offices.

Generator Hall, an enormous chamber excavated out of limestone bedrock, showing six turbines with one undergoing refurbishment.

A geology field class at Gardner Cave...

in Crawford State Park, Washington where university students learn cave science and mapping techniques. A former colleague invited me back into service given my long experience and expertise in the subterranean environment, and which turned out to be a thoroughly enjoyable two day-long project with a dozen undergraduate students.

Students learning to survey the illuminated upper part of the cave through which guided commercial tours are offered using tape and compass techniques.

Students recording carbon dioxide concentration in the cavern atmosphere.

Jazzed students exploring the wild, deeper part of the cave in a steeply descending passage. Note the flowstone false floor spanning sediments of glacial origin that were washed into the cave during the Pleistocene, and now are presently eroding by water flowing into the cavern from the surface.

Closeup view of delicate crystalline rimstone on the floor of the cave. Field of view is about three feet (one meter) wide.

Black and granular gold...

accumulates on the back deck below a double-chambered bat house. Some lucky gardener friend of mine is going to receive more than five pounds (2.3 kg) of premium organic free range bat guano in the near future.

Bats need friends! Provide free housing and they will eat insects and produce nitrogen-rich guano.

Camp buddies...

in a sub-alpine meadow near Butte, Montana where I spent the night on Homestake Pass. The air and sky were clear, the stars were brilliant, and it got wonderfully chilly.

Prairie dogs (genus Cynomys).

An enormous diluvial dumping...

from pluvial Lake Bonneville occurred through this gap in southeastern Idaho known as Red Rock Pass. The volume of the great gush is estimated at five thousand cubic kilometers (1,200 cubic miles!) of water, released about 14,000 years ago in a catastrophic megaflood that likely lasted weeks to months and scoured the Snake River Plain in Idaho downstream from this site.

Red Rock Pass, a few miles south of Downey, Idaho on US 91. View is to the south, or upstream during the big spill. The vast expanse of Lake Bonneville would have existed on the far side of the skyline ridge, reaching across a third of Utah. Once the rising lake water began spilling across this low point along its shoreline and into the adjacent valley, a great unraveling was unleashed. The unconsolidated surficial alluvium and the underlying sedimentary rocks forming the bedrock sill rapidly eroded, much as a dam collapses when overtopped.

Red X marks the spot (near lower right) of Red Rock Pass, the spillover point for Lake Bonneville. The torrent of floodwater exiting the basin through the gap lowered the overall lake level approximately 105 m (350 feet). Map from Idaho State University.

More here about this tremendous flood from the Idaho State University: Lake Bonneville flood.

A series of storm cells...

pass across Porcupine Rim this evening, and, unfortunately, nary a drop of rain fell in the valley. But fortunately there weren’t any lightening strikes. Here’s one storm cell, backlit by the setting Sun at dusk.

Happy 250 America...

as Castle Valley celebrates the semiquincentennial anniversary of the founding of our great nation on this Independence Day. Community tradition has the volunteer members of the Castle Valley Fire Department hosting a breakfast and parade, seen here featuring Engine 37 leading the way.

Cherry on top: Air quality this morning is the best since the summer solstice.

Read the Declaration of Independence.

Fire danger is very high in Castle Valley...

according to Smokey the Bear standing watch at the entrance to our community. The fire smoke in the air was so dense yesterday afternoon that if - goodness forbid - a fire had occurred in the valley, we’d have been largely unaware. Let’s be extra vigilant, folks!

No fireworks! And apparently Smokey still loves beaver, too.

Another smoky sunrise...

greets the dawn, the result of raging wildfires across the region. Air quality is unhealthy and getting worse.

Last night’s satellite image captured early in the evening showing fire smoke plumes and heat sources in southeastern Utah and Colorado.

MID-DAY UPDATE: Air quality continues to deteriorate throughout the day. Here are a couple of views around 1:00 pm MDT.

UPDATE at 5:00 pm MDT: Air quality has turned to very unhealthy. Round Mountain is no longer visible and the Tower has all but vanished from sight. Hell on Earth.

7:30 pm MDT: A late-day shift in the winds is driving the edge of the smoke plume across Parriott Mesa. Air quality is improving rapidly. Hallelujah!

A strawberry loving squirrel...

on the window sill, happily munching away on several strawberry slices I had placed out, hoping for its discovery. There are now two of these amusing creatures darting about and providing endless entertainment.

White-tailed antelope squirrel (Ammospermophilus leucurus).

Winds and light rains...

have washed the wretched fire smoke from the skies, returning the high desert to good air quality and allowing for the resumption of my early morning rides after a five day-long hiatus. Here’s my shadow claiming first tracks on the rain-dimpled singletrack this morning. Dee-lightful.

It's the one year anniversary...

of ordering the Bronco from the dealership in Moab and it just had its first oil change and tire rotation at around 5,000 miles (8,000 km). Big fun, both on and off road!

The custom-ordered Ford Bronco Badlands-Sasquatch with manual transmission arrived in Moab at the end of October and it’s been huge fun ever since, seen here parked below Adobe Mesa in April.