They Mapped Geologic Treasures

Lewis & Clark Geotour

Two hundred years ago, William "Strata" Smith was traveling the length and breadth of England, creating a map that changed the world.

At the same time, Captains Meriwether Lewis and William Clark and the Corps of Discovery were traversing the length of North America, creating other maps that changed the world as well.

In 1804, Lewis and Clark began a voyage of discovery with 45 men, a keelboat, two pirogues and a dog. They departed from Camp Wood in what was to become Illinois to explore, at the behest of President Thomas Jefferson, the lands involved in the Louisiana Purchase from France.

Lewis and Clark were ordered to write accounts of all they did, each species encountered, details of the cultures they met, maps of the land — everything. They traveled over a three-year period through lands that later became 11 states.

Strata Smith's human tale of endurance, dedication and achievement recently has been in the spotlight with the publishing of Simon Winchester's book The Map that Changed the World, chronicling the creation and presentation of the first geologic map.

And over the next two years, the bicentennial of Lewis and Clark's epic exploration of the Western United States will be celebrated in numerous festive and education events over the 3,200-mile trail from St. Louis to the Pacific Ocean.

One of the educational opportunities is the AAPG Lewis and Clark Geotour: Marias River to Gates of the Mountains, Montana, which will be offered July 12-17.

The trip will be led by William Hansen, of Jireh Consulting Services in Great Falls, Mont.

Image Caption

Lewis and Clark AAPG GeoTour slated for July 12-17, 2004

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Two hundred years ago, William "Strata" Smith was traveling the length and breadth of England, creating a map that changed the world.

At the same time, Captains Meriwether Lewis and William Clark and the Corps of Discovery were traversing the length of North America, creating other maps that changed the world as well.

In 1804, Lewis and Clark began a voyage of discovery with 45 men, a keelboat, two pirogues and a dog. They departed from Camp Wood in what was to become Illinois to explore, at the behest of President Thomas Jefferson, the lands involved in the Louisiana Purchase from France.

Lewis and Clark were ordered to write accounts of all they did, each species encountered, details of the cultures they met, maps of the land — everything. They traveled over a three-year period through lands that later became 11 states.

Strata Smith's human tale of endurance, dedication and achievement recently has been in the spotlight with the publishing of Simon Winchester's book The Map that Changed the World, chronicling the creation and presentation of the first geologic map.

And over the next two years, the bicentennial of Lewis and Clark's epic exploration of the Western United States will be celebrated in numerous festive and education events over the 3,200-mile trail from St. Louis to the Pacific Ocean.

One of the educational opportunities is the AAPG Lewis and Clark Geotour: Marias River to Gates of the Mountains, Montana, which will be offered July 12-17.

The trip will be led by William Hansen, of Jireh Consulting Services in Great Falls, Mont.

A natural storyteller, Hansen said the Geotour, which begins and ends in Great Falls, includes guided trips to the Great Falls of the Missouri River, White Bear Island Portage Camp, historic Fort Benton Missouri River steamboat wharf and a cruise boat trip through Lewis and Clark's "Gates of the Mountains" canyon in the Montana Thrust Belt.

The trip also includes outfitted white water and canoe trips.

Along the way there will be plenty of tales of the exploits — and a lot of geology. The exploration party spent over a month in the Great Falls area portaging the series of five, well, great falls.

As noted at Lewis and Clark sessions at last year's Geological Society of America annual meeting in Seattle, Lewis was the biologist/botanist who wrote in his journal in a narrative and descriptive style. Clark was the mapmaker/river man who wrote facts readably, with capitalization for emphasis and some inventive phonetic spelling.

With both having been tutored in the scientific method and observational skills, their journals contain hundreds of informative geological, geomorphologic, sedimentological and economic geology observations, Hansen said.

"Pretty good," he commented, "considering the science of geology hadn't even been invented yet."

Here's Clark's description of Giant Springs, June 18, 1805:

"We proceeded on up the river a little more than a mile to the largest fountain or spring I ever saw and doubt it is not the largest in America known. This water boils up from under the rocks near the edge of the river and falls immediately into the river eight feet and keeps its color for (about a) mile which is immensely clear and of a bluish cast."

Here's what we know now: At Giant Springs - Fresh water flows out of springs at 134,000 gallons per minute (1.93 million barrels of water per day) from a regional fracture system that conducts the water from the Mississippian Madison Limestone aquifer to the surface.

On entering the mountains on July 17, 1805, Clark described the rocks we now know are part of the Late Cretaceous Adel Mountain volcanics as:

"The immense high precipices oblige all the party to pass and repass the river from one point to another. The river confined in many places in a very narrow channel from 70 to 120 yards wide. Bottoms narrow without timber and many places the mountains approach on both sides; the river crooked, the bottoms narrow, cliffs high and steep. I ascended a spur of the mountain which I found to be high and difficult of access, containing pitch pine and covered with grass."

On entering the stretch of the river known as the Gates of the Mountains, Lewis writes on July 19, 1805:

"This evening we entered much the most remarkable cliffs that we have yet seen. These cliffs rise from the water's edge on either side perpendicular to the height of 1,200 feet. Every object wears a dark and gloomy aspect. The towering and projecting rocks in many places seem ready to tumble on us. The river appears to have forced its way through this immense body of solid rock for the distance of 5-3/4 miles and where it makes its exit below has thrown on either side vast columns of rocks mountains high.

"The river appears to have worn a passage just the width of its channel or 150 yards. It is deep from side to side, nor is there in the first three miles of this distance a spot except one of a few yards in extent on which a man could rest the sole of his foot. Several fine springs burst out at the water's edge from the interstices of the rocks. It happens fortunately that although the current is strong it is not so much so but what it may be overcome with the oars, for there is here no possibility of using either the cord or setting pole.

"It was late in the evening before I entered this place and was obliged to continue my route until sometime after dark before I found a place sufficiently large to encamp my small party. At length, such a one occurred on the larboard side where we found plenty of light wood and pitch pine. This rock is a black granite below and appears to be much lighter color above and from the fragments I take it to be a flint of a yellowish brown and light creamy-colored yellow. From the singular appearance of this place I called it the gates of the rocky mountains."

Hansen said the rocks Lewis described here are the Mississippian Madison Limestones, exposed in the footwall of the Eldorado-Lewis Thrust system in the Montana Thrust Belt.

Farther upstream, the Geotour will also examine the Precambrian Belt Series rocks thrusted over the Madison and exposed in the hanging wall of the thrust. Lewis describes the limestones as being dark and foreboding, which is probably a result of his seeing the rocks initially in the deep canyon in the early evening after a rain storm, which tends to make the rocks look darker.

One of the Geotour spots includes the Sacagewea Sulphur Springs, so-called because several gallons of the mineral-rich water was able to break a fever the courageous Indian princess had contracted.

And, on their return trip, the explorers took a wrong turn north into hostile tribal territory, which caused a backtracking again to the area.

One of the GSA sessions noted that the captains made some of the geological notations in greater than 45 percent of their daily journal entries in the out-bound 320 days of their journey, and exceeds 60 percent if their sedimentological observations are noted.

"This is a remarkably complete and relatively continuous account of the geological terrain of the expedition round," presenter John Jengo said, "and one that is simple to recognize and retrace 200 years later."

For information about the Lewis and Clark Geotour, contact the AAPG education department, or visit the AAPG Web site.