"The newspaper used to call the hills 'Little Upstart' or Tuality Mountains, of late they have been called the West Hills, which takes in the entire ridge towards Portland."

Wikipedia: Tualatin Mountains

The Tualatin Mountains (also known as the West Hills or Southwest Hills of Portland) are a range on the western border of Multnomah County, Oregon, United States.^[1] A spur of the Northern Oregon Coast Range, they separate the Tualatin Basin of Washington County, Oregon, from the Portland Basin of western Multnomah County and Clark County, Washington.

The highest peak in the range is Dixie Mountain at 1,609 feet (490 m).^[2][1] Other notable peaks include Cornell Mountain at 1,270 feet (390m), Council Crest at 1,073 feet (327 m), and Pittock Hill, location of the Pittock Mansion.^[3]

The hills date from the late Cenozoic era, and range up to over 1,000 feet (300 m). Composed mainly of basalt, the mountains were formed by several flows of the Grande Ronde basalt flows that were part of the larger Columbia River basalts.^[4] Human settlement goes back 10,000 years^{[citation needed]} to the area's earliest known residents, the Chinook people.^{[citation needed]}

Despite steep slopes, periodic landslides, and multiple earthquake faults, many residences have been built in the Tualatin Mountains, though much of the northern portion is undeveloped land within the 5,000-acre (20 km²) Forest Park. The landscape, inside and outside the park, is predominantly forested.

Tualatin Life: Tualatin Mountain Range – Lost in Oregon

According to Professor Burns, the Tualatin Mountain Range begins at the Coast Range near Scappoose, follows the Willamette River south as far as the Canby delta, including the gap at Willamette Falls. They were formed from volcanic lava flows about 7 million years ago. For thousands of years, the lava flows came down the Columbia River Gorge from the east near where the Oregon, Idaho and Washington borders meet. The lava flows, known as Columbia River Basalt, created peaks ranging at least as high as 1200 feet above sea level such as Council Crest, Cornell Mountain, Pete’s Mountain; hills such as the West Hills of Portland, Cedar Hills, and gaps such as at Lake Oswego and Willamette Falls. In the Tualatin Mountains also are volcanoes of the Boring Lava age that sit on top of the Columbia River Basalt: They are Mt. Sylvania, Cooks Butte in Lake Oswego, and the volcanoes above Cedar Hills. The lava flows would have been similar to current Mt. Kiluea flows on the Island of Hawaii.

The Columbia River Basalt lies under several feet of rich sand, silt and soils (loess) blown in by the winds over thousands more years. In addition, near the end of the ice age, Burns described even more soils, rocks and iceberg laden boulders (called erratics) were brought to the Tualatin Mountain foothills by at least 40 cataclysmic floods. The floods resulted with the melting and breaking of an ice dam holding back Lake Missoula. Each time, the lake waters emptied across Idaho, Washington and down the Columbia River Gorge. They traveled at speeds up to 60 miles per hour down the Gorge on their way to the Pacific Ocean but a basalt barrier at Kalama, Washington restricted the flow and backed the flood waters along the Tualatin Mountains as high as 400’ in what is now downtown Portland.

The raging flood waters entered the Lake Oswego gap of the mountain range and scoured out the lake before proceeding west into the Tualatin Valley going as far as Gaston and Forest Grove and the Yamhill Valley past McMinnville. They then raged further upriver and entered the Willamette Valley through a second gap in the Tualatin Mountains at Willamette Falls.

The 350-400’ high ice age floods waters backed up the Willamette River as far as Eugene, carrying the rich soils, debris and erratics (rocks that don’t come from here). The rich soils attracted pioneers to Oregon and are still key to Oregon’s agriculture. One note is that most current vineyards are placed above the rich soils 400’ elevation line in the valleys to keep the grape vines producing the flavorful grapes rather than mostly leaves and bushes. At the end of the ice age, over 12,000 years ago, ancient animals such as mastodons, mammoths, giant sloths, and bisons are a few of the ancient animals which lived on the land, proved from bones that have been found in the Tualatin, Willamette and Yamhill Valleys and radio-carbon dated. Many bones are being discovered and University of Oregon Museum in Eugene is a depository for the bones.

Unusual and interesting attractions worth seeing...

1) Canby Ferry on Willlamette River

2) Willamette Falls at I-205 overlook (and Mt. Hood in distance)-not far from where the Oregon Trail ended at Oregon City.

3) Field’s Bridge Park on the Tualatin River which describes the ice age floods and near where the Willamette Meteorite, the fifth largest in U.S. was found after it floated in an iceberg during the ice age floods

4) way down in the canyon below the TV towers is the Willamette Stone where the first survey of all Oregon lands began and where Meridians (north/south lines)-Meridian Park Hospital is on a meridian separating Washington and Clackamas counties) and Baselines (east/west descriptions to Idaho and Pacific Ocean at Bay City) were established in late 1800s.

5) At the Oregon Zoo, a geologic stratigraphic column can be studied by taking an elevator down into the Tualatin Mountain Range where the Metro light rail picks up riders going to the Tualatin Valley or downtown Portland.

6) On a drive along Skyline Ridge of the Tualatin Mountain Range, from the Zoo area to Scappoose, you can see the Portland Basin on one side and the Tualatin Valley on the other.

USGS: A Tunnel Runs Through It—An Inside View of the Tualatin Mountains, Oregon

The Tualatin Mountains form a northwest-striking ridge about 350 m high that separates Portland, Oregon, from the cities of the Tualatin Valley to the west. Known informally as the Portland Hills, the ridge is a late Cenozoic anticline, bounded by reverse faults that dip toward the anticlinal axis. The anticline is a broad, open fold consisting chiefly of Miocene Columbia River Basalt Group, with remnants of Miocene-Pliocene Troutdale Formation and Pleistocene basalt of the Boring Volcanic Field on the flanks of the anticline. Anticlinal structures similar to the Tualatin Mountains are characteristic of the northern Willamette Valley, where the structures accommodate margin-parallel shortening of the Cascadia fore arc. Global Positioning System (GPS) results indicate that the shortening is due to the northward motion of Oregon at several millimeters per year with respect to stable North America. Some of the uplifts may contain active faults, but the structures are poorly exposed and are overlain by thick Pleistocene loess and Missoula flood deposits. Between 1993 and 1998, construction of the 3-mile-long (4500-m-long) TriMet MAX Light Rail tunnel through the Tualatin Mountains provided an unusual opportunity to investigate the geological structure and history of the Tualatin Mountains. This report is a collaborative effort among the tunnel geologists and the U.S. Geological Survey (USGS) to document the geologic story and quantify late Cenozoic and Quaternary deformation rates of the Tualatin Mountains.

"The City of Portland sits at the confluence of the Willamette and Columbia rivers and occupies the western half of the Portland Basin and much of the adjacent Tualatin Mountains. The flat floor of the Portland Basin is punctuated by several small buttes and the Boring Hills, a complex region where small volcanic cones mix with blocks uplifted by faulting. The Tualatin Mountains, a straight and narrow range with a sharp, fault-bounded eastern edge, separate the Portland Basin from the Tualatin Basin to the west. The Tualatin Basin is generally flat, with a few faulted and folded highs in the center of the basin."

Tualatin is probably an Indian word meaning lazy or sluggish, this being the character of the river's flow. Other meanings are "land without trees", signifying the plains of Tualatin, and "forks" or "forked" for the numerous upper tributaries, including Gales and Dairy creeks.

Lyn Topinka, Columbia River Images

"Tualatin", "Twality", "Tuality" ... The name Tualatin is from Atfalati (rhymes with "quality"), the name of the Native American Kalapuyan tribe which once occupied the Tualatin River valley. Early settlers shorten the name to "Tualati" or "Tualatin".

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