Rattlesnake Mountain - What's in a Name?

By Ralph Owen

The Naming of Rattlesnake Prairie - First Version (A Tall Tale)

Sometime in the early 1980s Harvey Manning, founding president of the IATC and hiking guidebook author, and I tired of telling people on hikes that we led that we didn’t know why Rattlesnake was named Rattlesnake.  So we made up the following story to explain the name:

In the 1850s there were a series of Indian Wars (or as the American Indians called them the White-Man Wars) in what is now the State of Washington. Most of them were fought in Central and Eastern Washington. A group of U.S. Cavalry Soldiers came back over Yakima Pass returning from a battle in Central Washington. Yakima Pass, at the head of the Cedar River and south of Snoqualmie Pass, was the traditional horse route over the Cascades used by both the Indians and the Army. They stopped to camp for the night in a grassy area that now is the location of Rattlesnake Lake. One of the soldiers unrolled his bed roll in preparation to go to bed and a dead rattlesnake dropped out onto the ground. Evidently during the previous night in their cold camp in Central Washington it had crawled inside with the soldier to get warm and the soldier had not noticed it. It had been suffocated and died when the bed roll was tightly rolled up to pack that morning. The soldiers named this location Rattlesnake Prairie and the nearby mountain was later named Rattlesnake Mountain.

The Naming of Rattlesnake Prairie - Second Version

This version is from the book Pioneer Days on Puget Sound by Arthur A. Denny which was published in 1888.  Denny was the leader of the party that first landed on Alki Beach (West Seattle) in 1851 and has been called the “Founder and Father of Seattle” and was the founder of the University of Washington.

A party of men from Seattle set out on an expedition toward Lake Keechelus (or as Denny spells it Lake Kitcheles) in the early summer of 1855 looking for a route for a road through the Cascades from Seattle to Central Washington.  As Denny writes in his book: “At one time they were camping at what is now known as Rattlesnake prairie, and one of the party was startled by a rattling in the weeds.  He reported that he heard a rattlesnake, which on investigation proved to be simply the dry seed pods of a weed; but it was sufficient to give a name to a place which it has ever after kept.”

Rattlesnake Prairie Becomes Rattlesnake Lake

There was no lake at Rattlesnake Prairie in the 1850s at the time of the two naming stories above.  Rattlesnake Lake appeared in the spring of 1915 when waters inundated Rattlesnake Prairie and a small town located in the prairie.

In order to understand this flooding, it helps to know a bit about the City of Seattle’s Cedar River Water Shed.  In the late 1880s, after the big Seattle Fire, the Seattle Water Department began to realize that they did not have enough water for the people of the growing city and also not enough to fight large fires.  They began to look for an additional water supply and discovered the Cedar River.  By 1899, Seattle had acquired most of what is now the City of Seattle’s Cedar River Water Shed.  They began to use Cedar Lake, later named by Seattle as Chester Morse Lake as their upstream reservoir.  Cedar Lake was east of Rattlesnake Prairie and was about 600’ higher in elevation with the wall of a glacier side moraine left during the last ice age between the lake and the prairie.  Cedar Lake was drained by the Cedar River which had cut a course down through the gravels of this moraine.  The Cedar River continued downstream near, but not through, Rattlesnake Prairie.

In 1905, Seattle built a wooden dam, called the Crib Dam, near the downstream end of Cedar Lake.  This was done to increase the lake elevation from 1530’ to 1548’, both to increase the reservoir storage capacity of the lake and to increase the hydro-electric capability of a generating plant that was being built in the town of Cedar Falls by Seattle City Light.

In several years, Seattle realized that they needed both more water storage capability and more electricity for their growing city.  Seattle built a second dam a little ways downstream of the Crib Dam, but still in the upper headwaters of the Cedar River.  This concrete dam, called the Masonry Dam, was designed to initially raise the lake level to 1560.5’ and later to 1600’.  The dam was firmly anchored to solid rock below it and on its southern end.  The northern end of the dam was bordered by the gravels of the old glacial side moraine.

The Masonry Dam was finished by the spring of 1915 and the water level behind it slowly began to rise.  Before this time the small town of Moncton had been built in Rattlesnake Prairie.  Begun around 1906, when the Chicago, Milwaukee and St. Paul Railroad was built past Seattle Watershed’s town of Cedar Falls, by 1915 more than 200 people lived here.  As the water level began to rise behind the Masonry Dam, new springs appeared in the side of the moraine above the prairie and out of the ground within it.  Soon a lake began to appear within the prairie.  By May, the water was rising in Rattlesnake Lake a foot per day.  Houses in Moncton began to float off their foundations and into the center of the lake.  Seattle condemned the town of Moncton, paid off the residents and cleared most of the remains of Moncton out of Rattlesnake Lake.  Only a few foundations still exist in the bottom of the lake.  Most of Rattlesnake Prairie is now gone as it has become Rattlesnake Lake.

While the Cedar River does not flow into Rattlesnake Lake, the level of Cedar Lake (Now Chester Morse Lake), indirectly regulates the level of Rattlesnake Lake.  When Chester Morse is completely full the seepage through the gravels of the moraine raises the level of Rattlesnake.  By the end of fall, when the level of Chester Morse drops to its lowest level, the seepage stops and Rattlesnake’s level drops.

Houses flooded by the rising waters of Rattlesnake Lake, June 28, 1915. Photo courtesy Seattle Municipal Archive (7580)

Rattlesnake Lake from the ledge above. Photo taken during the during the historic Mountains to Sound Hike in July, 1990.