Tag: Rock Hounding

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Leaf Fossil Hunt

We’re getting close.

To a rockhound a cut bank rising from a road’s borrow pit draws attention. You might see a wall of stone, a tumble of gravel, or you may not even notice.

Rock pickers see these as a window to  the past. The road builder has conveniently opened a portal into local geology. 

Sedementary rock layers sitting exposed in a road cut

An important aspect of finding fossils and unearthing minerals is understanding time from a  geological prospective.

Sedimentary, igneous, and metamorphic are the three major rock groups. Knowing which type you’re looking at helps one understand what could possibly get chipped out.

Ochoco divide still recovering from wildfire

Understanding how the earth was formed is knowing a measure of geological time  .  .  .  literally millions of years.

This week’s trek took us to a road cut on the crest of the Ochoco divide. There we split apart sedimentary rock layers in search of leaf and twig fossils. 

This high up and still in spring colors

On the geological time line these layers are young, less than fifty million years old and likely encased in mud and sediment on an ancient lake bed.

Volcanic activity pushed these rocks up to form mountains, only to be exposed by a dozer cutting out a logging road.

Leaf fossil

Leaf fossils are one of the few types we’re allowed to collect  .  .  .  dig up some bones and authorities want to know about that. 

But plant material is fair game.  However, it’s not easy work. It’s a fragile dig. You need to carefully split layers of rock to reveal the fossil.

Most plant fossils are from impression fossilization. Layers of sediment and soil bury the plant material leaving an impression or copy showing  a leaf in rather fine detail.

However, there are  times when the plant material gets replaced with minerals and you get a cast fossil.

Often casts are with limbs or twigs and the mineral replacing the plant structure so that rather than a simple ‘image’ you have a physical copy  .  .  .  in rock.

Twig fossils

We picked through tailings and chipped away at rock faces long enough to get some representative examples.

There was no need to fill buckets with rock bound fossils. The goal is to explore some different places  .  .  .  well, and have a picnic in the wilds.

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Pockets full of Rocks

Rockhounding usually involves scrambling up hills

While many of our posts are about fishing, that’s not the only thing we enjoy.   We usually have a small menu of activities to choose from, while out on an adventure. 

Wandering the high desert of Central Oregon, it’s impossible NOT to marvel at its geological features. The streams we sit along, spent the last millennia cutting out those basalt-rimmed canyons.

High cliffs of Sutton Mountain, near Painted Hills, Oregon

The Cascade Range to the west and the sage steppe to the east of us is a landscape of volcanic oddities.

The “Wave” at Fort Rock

Central Oregon’s northern expanse of the Great Basin took shape about three million years ago (Pliocene epoch).

Volcanic eruptions and the formation of shallow lakes deposited the material that is fodder for rock hounders today. 

We’ve been picking over rock formations, digging pits and screening gravel beds for years.

It’s rare that we’ll come back from an outing without some samples in the back of the car.

Simple but essential gear

This week the focus of our trip was on rockhounding.

These June days are still cool enough to make scraping back layers of dirt and shifting through buckets of gravel bearable. 

The journey was pulled from one many geology related books occupying space on our shelves.

Rockhounding Oregon and Roadside Geology of Oregon are constant references when planning these early summer excursions.

In this case, a land owner allows access to BLM land across their property

This time around  .  .  .  our destination is Congleton Hollow and it’s 640 acres of BLM land which is open to rock collecting. 

Limb Casts are the target.  When a lava flow engulfs a forest the encased tree limbs turn to ash leaving a cavity which is eventually filled with minerals that over millions of years become agates.

Green and pink stones with distinct wood grain and sometimes bark patterns are the prize. But that reward is hard dug and often results only in fragments.

High Desert roads are edged in carpets of Lupine

The South Fork of the Crooked River runs along the lower reaches of Congleton Hollow. The upper slopes, where most of the rock searching takes place, are bare except for a scattered few juniper trees.

There are shade and grassy meadows at the base of the hill, on the banks of a lazy flowing stream.  

JQ has just the spot for this ‘boulder’ and she ferried it across a wide expanse to load it in the back of the car

We didn’t find a lot of Limb Casts, though JQ did lug back a large, stratified rock.

There’s no need for buckets of agates, and the point is to explore spaces. However, we always manage to leave with some rocks in our pockets. 

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More Rocks

Highway 20 ,,, clean air as far as the eye can see

Two things have happened . . . the air has cleared and daytime temps have dropped. So it is perfect weather to do some rockhounding.

There is no shortage of places to find fossils, minerals and rocks in Central Oregon, but all are nearly void of shade. Any roads near these sites will quickly become impassable with a day or two of rain. That in mind fall is an ideal season.

We’re headed east on US 20 to a dirt road just west of highway marker 77. Glass Butte and Little Glass Butte are six thousand acres open to public collection of a ‘reasonable’ daily amount of obsidian. The state defines reasonable as less than 250 pounds . . . no problem there.

The two low hills look like most of the hight desert landscape between Bend and Burns. A few patches of scrub pine and juniper amid large swaths of sage and rabbit bush.

Drive up the gravel road a few miles and quickly you start to see the glint of black rock scattered between the sage brush. Obsidian is typically black but at the Glass Buttes area you can find red, snowflake, green, and a number of other color combinations. This makes this a popular rockhounding site.

Shards of obsidian … this volcanic glass is hard, brittle and fractures with sharp edges.

We found a spot away from the crowds in the Little Butte area. It didn’t take too long to fill our bucket with marble sized pieces, perfect for the tumbler, and a few larger chunks as well. The material we picked up was mostly black but there are some with red and mahogany streaks. All were picked up off the surface with only minimal digging.

Once back home we rinsed the desert dust, inspected our finds and separated a load to polish in the tumbler. In addition to obsidian, we found some samples of petrified wood.

We’re thumbing through the Oregon Rockhounding book and plan more fall expeditions in the future.