Launch: CBig Arm Campground has a good ramp.

Nearby campsites:CRight at the ramp.

Comments: Flathead Lake is 50 miles long and 16 miles wide and covers 191.5 square miles - the largest natural fresh water lake west of the Mississippi River.


It's you to the left and I to the right,
For the ways of men must sever.
And it well may be for a day and a night
And it well may be forever
- Hovey


CCLife has some abrupt turns. Many are out of our control - things happen over which we can do nothing to prevent - totally unforeseen or not predictable. We refer to these as accidents or often, if health-related, fate. But there are other junctions in life over which we may have complete control … your choice of vehicle, vacation this year, person to marry. We just experienced one of those controlled junctions.
CCIt was actually pretty simple. We have been several months cruising the San Juan and Gulf Islands off the coasts of Washington and British Columbia. Season was advancing, we had a few doctor/dental things to do in Colorado, and friends to meet on Lake Powell next month - so we pulled from the salt water, scrubbed up the boat, got a few minor things repaired, and started on the four-lane heading to the south - destination? Utah and a short storage for Halcyon while we returned to Colorado. We stopped at a Rest Stop on I-90 just before the Interstates divide. I-90 continues to the east across Idaho and Montana and on to the Atlantic states. I-82 makes an abrupt turn to the southeast and into Oregon - our route to follow toward Lake Powell. I returned to the car before El, and a thought suddenly struck me from the blue - Flathead Lake. I had just pulled out the atlas when El returned.
CC"How about Flathead Lake for a few days before turning south? It's hot and really roasting down south - we could stay in the cool a little longer. It's only about 6-7 hours, it says in the atlas, so we could arrive before dark. It's supposed to be a pretty lake. What do you think?"

CCWell, it took El a little bit to suddenly think of making an abrupt turn. We ran through the changes this turn would involve - calling dentist and doc to change appointments, putting off 'stuff' we had thought needed doing back in Colorado, not seeing family for a few more weeks, … you know, the 'stuff' that keeps us anchored 'at home.'

CC"But we're 'at home' - most everything (except the dental chair) is on Halcyon. We can do 'stuff' on board swinging on a hook on a lake as easily as in Colorado (where we have a rental condo)."

CCYep, we got to the junction of Interstates and continued on I-90, and sure enough we arrived at Big Arm State Park on the west shore of Flathead Lake a few hours before dark.

El Setting Up Camp

CCWe set up camp (in the boat, posing as an R.V.) among the huge fifth-wheelers and mega-motor homes. As usual, folks stopped by to chat - some just to ask with disbelief, "You 'live' on your boat?"

CCEl loved to answer that question. "Yep, got everything a house has except space, and each of us can only sit in one chair at a time. And this house is a perfect R.V., has stayed at state parks all over the US, and then she can launch and float us off into the sunset."

CCMost folks walk off shaking their heads in disbelief. They have been conned by the culture into thinking that you had to pay at least six digits (and the first number is big) for a house, five or six digits for an R.V, and at least five (and maybe six digits) for a boat. Of course, after those costs, many had to limit the R.V.-ing and boating because there wasn't enough cash left over to use them. A few would stay to visit, often with the comment, "Well, I'll be darned. How do you do it?" and then we often meet some interesting folks and chat on while the campfire burns down to embers.


CCLakes don't belong. They are aberrations. And they are temporary. Think about it. Water runs down hill, we know that. Water cuts, and given some time, it cuts almost anything - even rock. So if there is a lake - a stoppage of the downhill run toward the ocean - of that powerhouse known as water - there must be a good reason. Ask yourself anytime you see a pond or a lake - why? What's the reason? The answer is often obscure but like many hidden treasures a gift to unravel and reveal.


Fact - No Man-made Dam

CCIn fact, it is the largest natural freshwater lake in the western United States. So the reason for its temporary existence must be fascinating - we think it is!

A Big One

Fact - The Rocky Mountain Trench

CCIt lies within the Rocky Mountain Trench, the Valley with a Thousand Peaks.
CCa) What's that? A narrow geological depression almost 1,000 miles long, extending from Flathead Lake all the way to the headwaters of the Yukon River in Canada. It parallels the steep western flank of the Rockies. Its rugged floor is 2-10 miles wide and it lies between 2-3,000 feet above sea level. The headwaters of the Kootenay, Fraser, Peace, Columbia and Liard Rivers lie in the Trench. It is easily seen from space photos.

CCCCb) What is the origin of the trench? It is formed by faulting. It is the surface reflection of a deep-seated ancient west-facing ramp with over 5 miles of vertical offset. This is an ancient crustal weakness, perhaps a former continental margin - perhaps an ancient plate boundary on the edge of the continent. The northern portion of the trench is dominated by strike-slip (side-by-side) faulting and the southern by normal (pull-apart by tension) faults. Important for commerce (railways, highways, river travel and Indian access to the continent from Siberia - why, even planes fly the trench since it is straight as a dye and heading almost north-south).



CC1. OK. So it lies in the Rocky Mountain Trench, a topographic depression, and that's a good reason for a lake. BUT, elsewhere in the Trench, rivers have followed a normal downhill pattern and cut a route out of the Trench and onward to the sea.

CC2. AND, they have here also. Flathead Lake is drained to the south by the Flathead River. BUT, why hasn't that river drained the valley? Why is there still a lake, a geological oddity? The fact that Flathead Lake lie in the Rocky Mountain Trench doesn't, by itself, answer the question, why the lake?

Cruising in the Trench

Fact - Modified by Glaciers

CCDuring the last (and perhaps former) ice ages, a huge river of ice filled the Trench. This big mound was part of the glaciers that buried the continent - hence their name - continental glaciers. High mountains, during the ice ages, developed local glaciers on their flanks - they flowed down mountainside valleys, carving and scraping as they moved. These glaciers restricted to mountains are called alpine glaciers. Here at Flathead Lake, the Mission Mountains on the east side of the lake supported alpine glaciers. They moved down the flanks of the range and joined the continental glacier flowing down the trench. The valley was filled wall-to-wall with a mighty continental glacier thousands of feet thick and more than twenty miles wide.

CCa) During the ice age, this huge glacier flowed southerly through the Flathead Valley. The massive continental glacier impacted the Mission Range from the north and was split into two branches by the Range - one branch moved southerly into the Swan Valley to the east and the other moved through the western valley occupied by Flathead Lake.

CCThe ice 'river' was so thick that it even covered the Mission range itself as far south as the lower end of Flathead Lake. Where buried, ice smoothed the summits, and to the south below the terminus of the ice, it couldn't smooth the peaks of the range, so they are craggy and rough.

Visualize a vertical line cutting the black island in two. On the range behind, all the summits to the left of the line are smoothed. Those to the right are peaks.

Glaciated by continentral glacier left; No continental glacier right

CCA little aside. When ice 'collides' with rock, it generally smoothes the side of the rock facing the ice, and rips out rock chunks on the 'downhill' side of the rock. One of the most prominent islands in Flathead Lake is Wild Horse Island. It is mostly composed of bedrock. Notice the profile of the island in the photo. The smooth side faced the ice, and the rough side was plucked by the ice leaving the bedrock mound.

Moved From Right to Left

CCb) The glacier ended about the southern shore of today's Flathead Lake. The ice was still moving southerly in the glacier, but it was too warm south of this area and so it melted the glacier as fast as it moved to the south. Glaciers carve the soil and rock it moves over and the resulting debris is carried in the ice 'river,' like a giant conveyor belt, and unceremoniously dumped into a pile at the terminus of the ice. This pile is called a moraine. Some of the debris is carried by streams as outwash and blankets the valley below.

The Red Arrows Mark the Division of the Ice Sheet into Two Lobes; The Yellow Line at the End of the Lake is the Moraine


Notice the low tree-capped ridge cutting across the lake at right angles to the Mission Range - that's the moraine

CC1. OK. So the pile of debris at the south end of the lake, left behind by the glacier, is a natural dam. Hence, the lake.

Looking south at the Natural Dam - the Moraine

CC2. BUT, the Flathead River cuts through the pile of debris. A breached dam doesn't impound a lake. BUT, by chance there happened to be a bedrock hill buried beneath the moraine where the water started cutting a 'spillway' through the moraine. As a result the meltwaters did not drain completely, allowing a remnant Flathead Lake to exist today in the valley once occupied by a glacier.

Note the Former Higher Lake Levels Before the Moraine Dam was Cut Lower

Fact - Stagnant Ice

CCa) As the climate warmed, the glaciers had less snow and ice to maintain themselves, and they stopped flowing. The ice age ended quickly according to age-dating techniques - a few thousand years and it was gone.

CC1. If the ice stopped flowing, and the ice that filled the Rocky Mountain Trench was many thousands of feet thicker than the ice covering the surrounding mountains, then the ice outside the trench would have melted away first leaving a great mass of stagnant ice occupying the Trench. Debris washed by meltwater streams would have bypassed the trench and deposited outwash beyond the stagnant ice filling the deep valley. Finally, most of the outwash was carried south (and it was), the ice melted in the trench (it did), the result would be a deep depression where the stagnant ice lay.



CCThat deep depression would fill with meltwater and make Flathead Lake. All lakes are temporary, so, of course, the Flathead River will eventually erode a valley through the outwash to the south and that will be the end of Flathead Lake, but meanwhile we have the beauty of the largest natural lake in the West.



CC The rocks surrounding Flathead Lake were formed in a world very different than we know today. They are ancient rocks from about 1.5 billion years ago. The earth’s environment was desolate, with no trees, fish, animals or birds. There was almost no oxygen in the atmosphere. Shallow seas with extensive near-shore flats were fed by streams that deposited great thicknesses of sand and mud. Rain frequently fell and pooled in vast shallow lakes and ponds in what would one day become northwest Montana.

CC Despite the hostile environment, blue-green algae mats often trapped fine particles of calcium carbonate to form structures called stromatolites, that grew in shallow nearshore environments. The surface of the rocks often display mud cracks, ripple marks, and, sometimes, the spatter marks of primeval raindrops.


Dendrite (Recent Groundwater Stain); Studying the Belt Series; 1.5 billion-year-old Stream Fluting

CC The earth’s crust slowly sank for about 100 million years forming a large geologic basin in which Belt Supergroup sediments accumulated as much as 10 miles thick! The rocks are common in northern and central Idaho and western Montana, and extend east to the Little Belt Mountains in central Montana. The sedimentary rocks along Interstate 90 between Lookout Pass and Alberton are almost entirely rocks of the Belt Supergroup. These rocks are distinguished by brown, gray, red, green, purple, and yellow colors and locally form dramatic cliffs where resistant, well-cemented sandstones are exposed in the canyon.


CC The growth of the Rocky Mountains is a perplexing geologic puzzle. The fact that an oceanic plate is in head-on collision with the westerly drifting North American continent is well substantiated with evidence. The problem is that mountain building in such a collision usually is focused between 200 to 400 miles inland from the subduction zone boundary, yet the Rockies are hundreds of miles farther inland. What geologic processes raise mountains at this distance from the plate collision boundary? Although geologists continue to gather evidence to explain the rise of the Rockies, the most likely hypothesis proposes an unusual subducting slab.

CC The illustration below shows an oceanic plate with a 'normal' subduction angle beneath a continental plate at a collisional plate boundary. The oceanic plate typically sinks at a fairly high angle (somewhat exaggerated here). A volcanic arc grows above the subducting plate.


CC This sketch shows the plate tectonic setting proposed for the growth of the Rocky Mountains. The angle of the subducting plate is significantly flatter, moving the focus of melting and mountain building much farther inland than is normally expected.


CC It is postulated that the shallow angle of the subducting plate greatly increased the friction and other interactions with the thick continental mass above it. Tremendous low-angle faults piled sheets of crust on top of each other (like sliding a deck of cards laterally), building the extraordinarily broad, high Rocky Mountain range.

CC Recent studies reveal two geologically recent very large earthquakes (of about 7.0 magnitude). Earlier discoveries suggest the earthquakes occurred 15,000 and 7,700 years B.P. Since those two quakes were about 8,000 years apart, and the last one was about 8,000 years ago, geologists suggest we’re due for another one.

CC In terms of seismic activity, Montana is second only to California. Missoula has a significant earthquake risk. And since Flathead Lake is a large lake a quake here could cause an inland tsunami.

CC Think twice about lake front property and maybe even the risk of cruising on Flathead Lake.


CCThis is certainly not a wilderness lake. Roads follow most of the lakeshore and houses line the shorelines. They are interesting in their variety.

The Grandiose and the Simple



Red-necked Grebe and Fawn


CCThere have been 79 sightings of the Flathead Lake Monster since 1889, according to Larry Hanzel, who has studied the monster. Ninety-two percent of the sightings have been between April and September. Seventy percent have described the monster as a large eel-shaped critter between 20 and 40 feet long. It is brown to blue-black and has large steel-black eyes. Larry worked for 17 years studying fish life in the lake, using nets and sonar. He never caught or reflected acoustic echoes off anything like the monster, but he did retrieve nets several times with large unexplained holes ripped in the nets.

CCThe best year for sightings was 1993, with 13 reports. Eighty percent of the sightings were by more than one person. In May, two monsters were seen together, by two different reports. In July, two sightings occurred within 25 minutes of each other. Six sightings that year reported swarms of bait fish jumping out of the water (to avoid being eaten?).

CCReports have been submitted by first-time visitors as well as long-time residents. "Mothers, doctors, lawyers, biologists, engineers, anglers and policemen" all have reported sighting. Mr. Hanzel asks all to be observant and to report sightings to him.


Former Sightings of the Monster; "Off the Point - There! - Is That It"


We had a delightful time on the lake, all because of the road not taken.

Sundown on Flathead


Two roads diverged in a yellow wood
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth.

Then took the other, as just as fair,
And having perhaps the better claim
Because it was grassy and wanted wear
Though as for that, the passing there
Had worn them really about the same.

And both that morning equally lay
In leaves no feet had trodden black.
Oh! I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back
I shall be telling this with a sigh
Somewhere ages and ages hence
Two roads diverged in a wood, and I …
I took the one less travelled by,
And that has made all the difference.
- Frost


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