- Basking in the Boulder Batholith
- by George Everett
- One of the most
pleasurable aspects of living in Butte is that it is surrounded
by Montana in every direction, and some of the state's wildest
and most scenic parts at that.
Complex geology is to blame; it has made Butte what it was and
what it is. Butte is in the heart of a huge granite formation
called the Boulder Batholith that stretches from south of Helena
to north of Dillon. The Batholith was shaped by magma shoved
upwards by volcanic eruptions about 60 to 70 million years ago.
Then, granite (quartz monzonite) was pushed to within a few miles
of the surface before rapid cooling stopped it and caused cracks
and fissures to occur. Into these cracks flowed mineralized solutions,
most likely from the molten magma below, containing copper, gold,
silver and other now precious metals.
The same geology responsible for Butte's underground mineral
wealth also created the wild variety of rock croppings on the
surface. Soil that once covered the Batholith has long since
eroded, exposing rock croppings in bizarre shapes and sizes.
Within a half hour drive south of Butte, the Humbug Spires near
Divide stand as eerie evidence of these prehistoric upheavals.
Look for huge spires rising along the western edge of the Highland
Mountain range easily visible from Interstate 15.
In other places, protruding rock croppings resemble the teeth
of a giant in sore need of orthodontics. To the East of Butte
over Homestake Pass on I-90 the Batholith results in a crazy
assortment of ruddy boulders on the east side of the pass that
is known locally as The Dragonback.
A couple miles
north of the Pipestone Exit on I-90 on Route 222 is Spire Rock,
a popular attraction for rock climbers. Nearby, marked only on
topo maps is Ringing Rocks, a strange boulder pile that attracts
light hearted skiiers and hikers with hammers who make real "rock"
music by banging on them like a Flinstonian xylophone. There
is a similar formation in a state park in Pennsylvania, too where
the rocks sound exactly like the music created in the hills near
Southeast of Butte, you can drive through more of the Batholith
by taking Route 2 toward Whitehall. The stretch from Thompson
Park to Pipestone Pass is known as Harding Way and it is one
of the best engineered roads in Montana with
cross-country skiing on marked trails and the old Milwaukee Road
rail bed on the pass.
Here, look for tall trees growing between boulders. On a closer
look, you'll notice that the trees are actually growing from
crevices. Soil blows into the fissures (called joints) and soon
seeds follow that allow huge pine trees to flourish. After wind,
rain, and ice, it is yet another way that the rocks are worn
down to elemental gravel and then soil.
Resilient seeds germinate and sink roots in shallow soil in the
crevices and grow tall until the wind inevitably topples them.
Meanwhile the boulder that nurtured the tree has split and separated
forever with no trace of what drove the solid rock apart.