When a botanist must be a geologist

Geologic map of Wyoming; Love and Christiansen (1985); click image to view.

“A geologic map is a portrait of the surface of the Earth ... This map of Wyoming shows, in a very general way, the distribution of rocks and sediments across the face of Wyoming, scrubbed clean of its thin veneer of plants and soil. [horror of horrors!! ... italics added]  From Wyoming Geomaps by Sheila Roberts, Geological Survey of Wyoming, 1989.

This week is Earth Science Week and the theme for 2013 is Mapping our World -- to “promote awareness of the many exciting uses of maps and mapping technologies in the geosciences.”  Geologic maps are indeed critical in my profession.  But I’m not a geologist, I’m a field botanist.  In Wyoming, we often rely on geologic maps to study plants.

I was lucky to start my career when the flora of Wyoming was still relatively poorly known.  At times I felt like a 19th-century naturalist, roaming through unknown territory in search of new knowledge.  The projects I enjoyed most were rare plant surveys.  Many species then on Wyoming’s rare plant list were known only from a few specimens in herbaria.  We had little clue as to their real status.  Surveys were designed to answer the following:  Is the species indeed rare?  What’s its habitat?  How widespread is it?  Are there threats?  Given limited funding and time, it was critical to maximize chances of finding populations.  Often this required use of a geologic map.

Cary’s beartdtongue (Penstemon caryi) grows in areas underlain by calcareous rocks in the Bighorn Mountains.  Photo by Andrew Kratz; courtesy USDA Forest Service.

Quite a few of our rare plants are edaphic endemics.  Endemics are restricted to specific areas or habitats; edaphic endemics grow on specific soils or rock types.  In Wyoming, they are especially common on calcareous rocks -- limestone and dolomite (yes, rare plants can be common, more discussion below).

Wyoming rare plants endemic to calcareous habitat, by mountain range.

Fortunately for rare-plant botanists, most mountain ranges in Wyoming have calcareous rocks exposed on their flanks.  The following diagram of the Wind River Mountains shows why -- these are Laramide-style uplifts.

Section through Wind River Mountains; Paleozoic and Mesozoic sedimentary rocks exposed on northeast flank.  Regional Geomorphology class notes; Dr. Brainerd Mears, Jr., Univ. Wyoming, 1984.

Below is a geologic map of the Bighorn Mountains and vicinity.  The light blue map unit includes limestone and dolomite.

Modified from Love and Christiansen (1985).

Note the similar pattern in the next map.  These are collection sites for rare plants endemic to limestone and dolomite -- calceophiles.

Map from Wyoming Natural Diversity Database (WYNDD), 1988.

Obviously a botanist who understands and can use geologic maps will be better at rare plant surveys!

Shoshonea (Shoshonea pulvinata) grows on limestone, for example above the Clarks Fork Canyon in northwest Wyoming.  Note round green patches in foreground of photo above.  Surveying rare plants on the flanks of the Absaroka Mountains was one of my more spectacular projects.  Photos above and below courtesy WYNDD.

In the right habitat, i.e. on the right rock type, edaphic endemics often grow in profusion.  Sometimes it’s difficult to convince people that these really are species of concern.

Shultz’s milkvetch (Astragalus shultziorum) often forms extensive stands at the base of dolomite and limestone scree slopes in the Salt River Range.  Photos above and below courtesy WYNDD.

Flowers ca 12 mm long.

Most or maybe even all of our edaphic endemics are thought to be neo-endemics (recently evolved), suggested by their restricted distribution and local abundance.  When did they appear on the scene?  Surely it was after the last ice age.  During the Pleistocene much of Wyoming was in permafrost or under ice.  We can only speculate of course, but what a wonderful thing to do while wandering in search of rare plants.

Aromatic pussytoes (Antennaria aromatica) occurs as scattered populations on limestone in mountain ranges in western Wyoming.  The leaves smell of citronella or orange peels when crushed.  Photo courtesy WYNDD.

How the Palouse was Lost

On the Outlaws Trail by Sharon Bodily.  Available at Western Art Association Auction Art.

“I tell ya Tom ... there was a time when these hills were all in grass, rich and lush and filled with flowers in the summer.  Deer and cattle grew fat, there was plenty for all.  Then came the farmers.  They fenced, they plowed, they built houses, roads and towns.  I miss the old times.  They were wild, there were outlaws, a man had to fend for himself ... but at least he was free.”

There’s a kind of grassland in eastern Washington and adjacent Idaho called Palouse Prairie, growing on rolling hills of windblown silt called loess.  Where the loess came from is debated.  Perhaps it was deposited by dust storms during an arid windy interglacial period (Allen et al. 2012).  In any case, the loess forms a thick blanket up to 250 feet thick on top of basalt bedrock (Bjornstad 2006) over an area of many hundreds of square miles.

The Palouse (pah-LOOS); from Wikimedia Commons.

Today's Palouse Prairie in the fall.  Source.

Loess soils are deep and fertile and ideal for grasses.  That’s why the Palouse has largely disappeared -- most of it was plowed and planted with domestic grass (wheat) in the late 1800s.  Like so many North American grasslands on fertile soils, the Palouse Prairie is now an endangered ecosystem (Looney and Eigenbrode 2012).

Photo by Anne McKinnell from her 8 types of Light ebook (recommended!); used with permission.

But farmers were not the only factor in destruction of the Palouse.  There was a time even further back when not only grassland was destroyed but the loess as well.  It was a different time, colder, snowier, with herds of giant beasts roaming the prairie -- caribou, mammoths, long-haired bison, camels.  The rolling grasslands extended uninterrupted for as far as a mammoth or perhaps a hunter could see.  This was during the last glacial advance, at the time of the great floods.

If you’ve been following this series of posts, you know that 15,000 to 18,000 years ago 1) a lobe of the Cordilleran ice sheet extended as far south as Sand Point, Idaho; 2) it impounded a lake of gigantic proportions -- Glacial Lake Missoula; 3) it repeatedly failed; 4) some of the resulting floods were massive, swift and destructive at a scale hard to imagine.  Water hundreds of feet deep roared across eastern Washington at speeds of up to 60 or even 80 miles per hour, traveling some 500 miles to the Pacific coast in only two or three days!

This much water traveling at these speeds is powerful enough to scrape, scour and carry away plants, soil and dirt all the way down to bedrock.  An estimated 16,000 square miles were ravaged, producing mosaics of grassland and scabland, best appreciated from the air.

Anastomosing channels of the scablands; from Google Earth, click photo for better view.

The braided, anastomosing patterns of exposed basalt are highly suggestive of flooding.  Channels split then reunite, very different from familiar drainages where smaller streams consistently join to make larger ones flowing downstream.  The pattern of scabland channels looks very much like “water seeking its way over fresh terrain” in the absence of established drainages (Allen et al. 2012), for example when a creek flows across constantly refreshed sand to the sea.  These patterns are easy to see from the air, but they were first recognized as flood topography before aerial photos were available, by geologist J Harlan Bretz (1923).  At that time, a catastrophe at such a scale was quite a conceptual leap, and many years passed before others accepted his explanation.

You can experience the mosaic of loess and basalt by driving across eastern Washington.  At first the wheat fields seem unending, but then dark objects appear low on the horizon, becoming scattered pines on rough black rock.  Then it’s back to wheat fields -- the Palouse of today.

After all the wheat, we were excited by our first scabland experience, though it was pretty tame compared with what came later!

Scabland in the Telford tract off Interstate 90.  Once/if our government shutdown ends, you can google Telford Washington BLM for more information.

Ponderosa pine in scabland.

This post is part of a series about the Ice Age Mega-floods of the Pacific Northwest.

Sources

Allen, JE, Burns, M, and Burns, S.  2009.  Cataclysms on the Columbia.  Portland State University, Ooligan Press.

Bjornstad, B.  2006.  On the trail of the ice age floods.  Sandpoint, ID:  Keokee Books.

Bretz, JH.  1923.  The Channeled Scabland of the Columbia Plateau.  J Geol 31:617-649.

Looney, C, and Eigenbrode, SD.  2012.  Characteristics and distribution of Palouse Prairie remnants.  Nat Areas J 32:75-84.