November 22, 2022

Since last week’s bitter cold, it’s warmed up gradually. This afternoon at Missoula’s Greenough Park, it’s actually a few degrees above freezing. Where we’re standing near the DNRC streamflow gauge, Rattlesnake Creek is about two thirds covered with a milky layer of ice. We can see the water slipping and swirling under the ice. An occasional air bubble or cottonwood leaf drifts past in the current. Among the cobbles of the stream bottom, several shadowy trout are resting, maintaining their spots with an occasional flick of a tail.

It’s easy to notice the wintry stream, burbling and gushing icily past the cottonwoods and the red-osier dogwoods. But what’s practically impossible to see or even imagine is what’s happening underground. The water doesn’t end at the streambanks. We’re standing on it, too. Just a few feet below us is the aquifer. It’s a slow-moving river of water within the ground, moving much slower than the stream, water percolating invisibly through layers of sands and gravels, its temperature stabilized by the embrace of the earth.

I’m here today with the Watershed Education Network (WEN) to get a glimpse into this invisible, underground, watery world. Throughout Greenough Park, there are 15 groundwater monitoring wells that WEN has been checking on since 2015. Each well gives us a narrow glimpse into the aquifer. We already know the precise elevation of the ground surface at each monitoring location. And today we’ll be measuring the water level in each well. By combining these two pieces of information, we’ll get a three-dimensional map of the groundwater surface.

Groundwater and the stream connection

Water flows downhill – and that’s true for water within the earth, too. So by seeing where the groundwater surface is higher and where it’s lower, we can understand which way it’s flowing.

In Greenough Park, Rattlesnake Creek is like an interstate highway for water. The flow is so fast that we can hear its rush. In comparison, the aquifer under our feet is like a web of unmaintained Forest Service roads. It’s very slow going for the water. As the stream sweeps past, the groundwater shifts slowly.

But the water under our feet and the water in the stream are intimately connected. At times, the flow is from the stream to the aquifer. At other times, the aquifer flows into the stream, buffering the creek’s inhabitants from extreme temperature fluctuations.

Today, besides checking the groundwater wells, we’ll measure the surface elevation of Rattlesnake Creek in several places.

“That gives us a really good idea of how groundwater and surface water interact,” says Brook Bauer, WEN’s citizen science coordinator.

And in this section of Rattlesnake Creek, there’s a lot of interaction between the aquifer and the stream. During high water in the spring, the flow is generally from Rattlesnake Creek into the surrounding aquifer, rehydrating the sands and gravels under our feet. In the fall and winter, when the stream is lower, groundwater is usually flowing back out of the aquifer into the creek – helping support all of the trout, mayflies, and caddisflies that depend on the in-stream flows.

Checking the wells

This afternoon we split into two teams to check all 15 wells. Brook Bauer goes south with Kat Leister, WEN’s communications coordinator, and Rita Goerlich, a frequent WEN volunteer. Stephie Novak, WEN’s Stream Team coordinator, heads north with me and Kevin Mobley, a University of Montana student completing his degree in environmental studies and history.

Our first well proves easy to find, the metal plate exposed in an area where the snow has melted. We have more trouble finding some of the others on this wintry day. We know approximately where all of them are – but searching for a saucer-sized metal cover under a few inches of snow makes for a frosty sort of scavenger hunt. 

Besides tools for opening the well covers, we’re carrying a well tape with us. It’s a $600 electrified tape measure on a reel. When the sensor at the tip makes contact with the groundwater in the well, it completes a circuit, triggering a piercing electronic squeal. Then we carefully note the measurement where the tape crosses the top of the well casing. This gives us our groundwater elevation.

“It’s a lot better than dropping a stick down a well,” Stephie says. 

The warmth of the earth

The wells are scattered across Greenough Park, some near the stream and others farther away.

“Do you ever have a problem with the groundwater freezing?” Kevin asks.

Stephie tells us that, for most of the wells in the park, that shouldn’t ever be a problem. The temperature-moderating effect of the earth is incredible. The very top layers of the ground freeze during the winter, but that’s it.

“For it to get multiple meters down to the groundwater is pretty unlikely,” says Stephie.

Closer to the creek, where the ground elevation dips and the aquifer is much closer to the surface, it might be possible for some of the wells to freeze during a cold snap. But the temperature-buffering properties of the earth extend to the stream, too. As temperature-stabilized groundwater seeps into Rattlesnake Creek, it reduces the stream’s tendency to freeze in the winter and to overheat in the summer.

Floods and base flow

I ask Stephie what happens to the groundwater during rainy, fast-warming springs when the streams run bank-full and the rivers flood. But I’m surprised to learn that flood years have only minor impacts on groundwater. 

“We had a massive flood year in 2018,” Stephie tells us. 

The floods made a big difference in the stream itself. 

“We got to see huge changes in channel shape.”

But, once again, groundwater moves slowly. A flood on the Rattlesnake Creek “interstate” passes in the blink of an eye compared to the pace of the groundwater. The torrents sweep past in a rush, without much time for the waters to seep in and recharge the aquifer.

We’re checking our last well now. This one is just a few feet from the edge of Rattlesnake Creek – and during spring floods, it can actually be submerged by the stream itself. It’s just another demonstration of how intimately groundwater and streams are linked.

The riffles of Rattlesnake Creek rush and foam soothingly behind us as we cap the well and pack up the well tape. According to the DNRC stream gauge, the flow of Rattlesnake Creek has more than doubled since last week, no doubt as our sunny afternoons have melted some of the snow in the watershed. But during the low flows of September, when the snowpack is long-gone and the rain showers are scarce, Rattlesnake Creek keeps flowing, providing homes for bull trout, whitefish, and a diversity of insects. Why? 

Groundwater. It’s the base flow that keeps the stream going during the dry season. It percolates at its gentle pace from rocks, gravels, and sand lenses throughout the Rattlesnake Creek drainage.

The world of groundwater

Rattlesnake Creek, it turns out, is much larger than I ever would have imagined. It’s not just the visible expressway of the stream itself, but also the slow, hidden underground flow we walk on. Together, they form one complex, dynamic system. Sometimes, the groundwater feeds the stream; sometimes, the stream recharges the groundwater. And what goes on in the Rattlesnake Creek system is a microcosm of the relationship between groundwater and surface flows within and underneath Missoula itself. The surface streams – including Rattlesnake Creek, the Clark Fork River, Miller Creek, and the Bitterroot River – are all connected to vast, slow, complex underground flows, seeping through the earth underneath our roads and houses.

These underground flows form the aquifer that we drink from.

“We get all of our water from the aquifer,” Stephie tells us.

The world of groundwater is hard to imagine – but it surrounds us every day. And afternoons like this one, mapping out the groundwater surface and its relationship with a stream, can help us imagine and understand what our eyes can’t see. 

So next time you walk by a stream, turn on the tap, or drink a beer brewed in Missoula, take a moment to imagine the aquifer beneath us. It may be unseen, unsung, and nearly impossible to picture. But we wouldn’t be here without it.

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November 17, 2022

It’s a cold, sunny morning in the parking lot of Missoula’s Greenough Park. There are eight of us gathered here, carrying binoculars or magnifying glasses. We’re here for the Montana Natural History Center’s monthly naturalist saunter. Our goals for the morning are simple: be curious, observe, and get to know some of the stories of this place.

It snowed lightly last night. Now the thermometer at the airport reads 23°F, but it’s probably colder here, in the narrow valley of Rattlesnake Creek. 

I was in a hurry this morning, and now I’m mentally kicking myself for arriving so unprepared. I ran out of time to put my boots on. Instead I’m wearing a pair of worn-out hiking shoes and just two light coats. The only camera I have with me is my phone. My gloves are lightweight and slightly damp from the day before. But if a song sparrow can survive a whole winter out here with nothing but its feathers, I can probably be out here underprepared for an hour or two.

Naturalist Ser Anderson is leading this morning’s saunter. It’s is an opportunity for us all to get to know the winter landscape better. Whenever we’re out in nature, we all bring different perspectives and notice different things. 

“It makes this a really valuable experience to gather together,” Ser says.

Dippers and chickadees

It doesn’t take long to see this in action. By the time we’ve been walking for a minute, we’re already learning from each other about the creatures of this urban park. We stop at the footbridge over Rattlesnake Creek, where Ser has seen a pair of American dippers nesting for several years. Ser scans upstream and down, looking for a well-camouflaged, stream-dwelling gray bird with a buzzy call. But the dippers seem to be in another section of the stream today. Ser tells us that they see dippers here year-round. If Rattlesnake Creek freezes during a cold spell, these cold-hardy stream-dwellers will move downstream to the Clark Fork River. Otherwise, they seem to prefer foraging in the smaller streams, such as Rattlesnake Creek. 

Nate Johnson notices a narrow line of tracks across a snow-covered island in the creek. Could these be dipper tracks? It’s a thin trail through the snow, and the prints seem to alternate with each other. The trail is much too narrow for a mink or a muskrat, and the pattern doesn’t look right for a deer mouse or a vole. We can’t be sure, but an American dipper seems like a good guess.

While we’ve been scanning the creek for the elusive dippers, a mixed flock of black-capped chickadees and pygmy nuthatches has been keeping us company, flitting around the trunk of a large cottonwood near the creek. It’s another mixed-species winter flock, something we can expect to see frequently through the rest of the winter. Besides chickadees, nuthatches, kinglets, and woodpeckers, Ser mentions that they sometimes see jays joining these mixed-species groups.

Birds and plants in the cold

The wind is blowing plumes of snow off of the crest of Mount Jumbo above us. In spite of the sun, it’s cold. My toes are starting to complain. The rest of my body is asking me why I didn’t put another coat on this morning. I’m nowhere near the slippery slope towards hypothermia yet, but the morning would have been much more comfortable if I had planned ahead a bit more.

The cheerful calls of the chickadees seem to mock my discomfort. If they’re cold, they aren’t telling me. And even more amazing are the dippers. They plunge and swim through the ice-cold waters of the stream throughout the winter. For the dippers, this penguin plunge is their buffet: caddisflies, mayflies, other aquatic invertebrates, and perhaps even small fish are their year-round foods.

We stop to look at a patch of common snowberries (Symphoricarpos albus) growing next to a young grove of Norway maples (Acer platanoides). This unusual mixture is part of what makes Greenough Park interesting, Ser tells us. 

“It’s a fascinating combination of native species and non-native species,” they say.

Native plants like snowberry, yarrow, and cottonwood mix with garden escapes like Norway maple and European mountain-ash (Sorbus aucuparia). It’s a reflection of how much we’ve changed the landscape, colonizing it with houses, European plants, and pavement. But it also shows us how resilient native plants can be. A half-wild park like Greenough can be a refuge for biodiversity. It’s not pristine – but compared to a lawn or a parking lot, there’s a lot of habitat here.

Snowberries and hawthorns in Greenough Park

Fruits still hang from the snowberries in luminous white clusters. What eats snowberry fruits?

“Not much until they’re desperate,” Ser tells us. They’ve seen pine grosbeaks eating these fruits in January, when there’s not much else to eat. Indeed, this seems to be one of the biggest advantages of snowberry fruits. They may be mealy and mildly toxic to humans – and apparently they’re not especially tasty to birds – but they stay around throughout the cold season. Unlike the fall fruits, like elderberries and chokecherries, snowberries are still here when the cold gets bitter and any calories are important, whether they’re especially tasty or not.

Fall and winter fruits continue to accompany us on our meander through Greenough Park. We stop to look at a snow-capped nest in a hawthorn (Crataegus sp.). It’s conspicuous now that the leaves have died back. A bulky cup woven of grasses, it’s perched high in the hawthorn, close to the main stem. It’s the size of a large orange, almost directly over the busy pedestrian trail. Winter nest identification is a difficult skill, and no one in our group is very experienced with it. But based on the size, construction, and location, we suspect that this nest belonged to a pair of American robins.

The hawthorns in the park seem to have lost their fruits already. Did the birds eat them this fall, or was this just a bad year for hawthorn fruit set? Ser reminds us that, besides fruits, hawthorns offer a variety of other advantages to wildlife. Black-billed magpies commonly build their bulky stick nests among these thorny branches, where they’re well-protected from predators. And northern shrikes may impale their prey – mostly mice and voles – on the thorns.

Red-osier dogwoods and Rocky Mountain maples

Just a few yards from the hawthorn, we take a look at a red-osier dogwood (Cornus sericea), its deep red branches standing out against the snow. Its small, bitter white fruits are gone already. But earlier in the fall, Ser often sees pileated woodpeckers eating them. It’s a comical sight. The bulky, red and black woodpeckers can’t perch upright on the slender dogwood branches, so they tip upside down as they snatch the juicy fruits. And the pileated woodpeckers aren’t alone. Around Helena, I’ve seen white-crowned sparrows, American robins, and black-capped chickadees stocking up on red-osier dogwood fruits during fall migration.

But that season is past now. Half a foot of snow covers the ground, and the dogwood branches are bare. But even in the winter, we can learn to recognize these bushes by the personalities of their branches and buds. Ser points out that the winter red-osier dogwoods can resemble another of our native shrubs, Rocky Mountain maple (Acer glabrum). Both have branches that depart from the stem in opposite pairs, and both can have beautiful, reddish twigs.

So how can we tell these two apart? The buds provide one secret. Red-osier dogwood buds are elongate. Ser describes them like a pair of tiny prayer hands. Rocky Mountain maple buds, on the other hand, are rounder and fatter, protected by more bud scales.

Getting to know the bedrock

We slow down again as we pass by an exposed rock outcrop, jutting out towards the trail. Marilyn and Don Cook admire the rocks and marvel at how they came to be here. 

“My mind stops functioning past a few thousand years,” Ser says. It’s a similar experience for me: the immensity of geologic time is impossible for me to truly comprehend. But even though none of us are geologists, and our understanding is limited, it’s worthwhile to take a look at this outcrop. We notice that the rocks are arranged in rusty orange strata that dip towards the south. 

Later, I look at a geologic map and learn that this outcrop belongs to the Snowslip Formation, a layer of sediments laid down over a thousand million years ago. Tipping rock layers like these are a common sight in the Rocky Mountains. Originally, these rocks were deposited in level layers, the sediments carried off of the eroding mountains. But over time, immense and slow pressures tipped them, angling them southwards, as regional forces faulted and folded the bedrock up into new mountains.

But even without the geologic map – and without the ability to imagine a billion years – we can tell that these rocks are offering a unique habitat for creatures in the present. The south and east faces of this outcrop are bare rock, baked every day by the sun and scoured by rain and gravity. But where the rocks extend northwards in an overhang, where the water drips slowly and the sun doesn’t shine, a miniature garden of mosses and lichens are growing. In the early spring, perhaps the American dippers will venture here, gathering these mosses to build their sheltered nests under the footbridges that cross the creek.

Greenough Park’s waxwings

A soft, high-pitched chorus in the cottonwoods draws our attention away from the rock face. It’s a flock of cedar waxwings, their pale yellow bellies glowing in the morning sun. Ser spots a couple of Bohemian waxwings with them. Once in a while, we can hear the musical trills of the Bohemian waxwings mixing with the softer lisps of the cedars. It’s a different sort of mixed-species winter flock than the chickadees and the nuthatches: these birds are focused on fruits.

Cedar waxwings nest here in the summer, and some of them remain around Missoula through the cold season. They group up in the winter and shift their diet, from mostly insects to almost entirely fruits. The Bohemian waxwings, the larger, grayer cousins of the cedar waxwings, are strictly winter visitors to Montana. They nest in the boreal forest, moving south as the weather gets cold. Like the cedars, now they’re very focused on fruits.

So what are the waxwings doing in the top of this cottonwood, perching among its bare, fruitless branches? We notice a pattern of movement: a few at a time, the waxwings are gliding down from the cottonwood into the undergrowth. At the same time, others are flying back up to this conspicuous perch. Sure enough, as they land again, we can see that the waxwings are carrying bright orange fruits in their beaks. They’re feeding on the European mountain-ashes – one of those garden escapes that is common in Greenough Park. And if the waxwings are any judge, it seems that the mountain-ash fruits are tastier than the snowberries. Presumably, this flock is digesting their meal high up in the cottonwood so that they can watch for sharp-shinned hawks, merlins, and other predators. 

Elderberries and nightshades

Fruits and birds continue to accompany us as we wander through the park. We stop to look at the elderberries (Sambucus cerulea). The transition from fall to winter happened so fast this year that we can still find clusters of their powdery-blue fruits, drooping in the cold. Normally, the birds clean up the elderberries before winter arrives.

We pay attention to the hollow, pithy elderberry stems. They break off easily, giving these shrubs a rather disheveled appearance. But though they may not look very tidy, the elderberry stems are important. While many of our native bees nest in the ground, an important assortment spend most of their lives in twigs just like these. For example, bees in the genus Ceratina may overwinter in elderberry stems, hidden from sight, waiting quietly for spring to arrive.

We can still hear the waxwings trilling and lisping as they feed on the nearby mountain-ash fruits. A black-capped chickadee flits past us, probing busily for insects and spiders among the shriveled brown alder leaves that still hang from the branches. A song sparrow gives its chimp call from the thicket near us.

A slender, woody vine droops with shiny clusters of juicy red fruits near the trail. What is this? It’s bittersweet nightshade (Solanum dulcamara), a relative of tomatoes. Native to Europe and parts of Asia and northern Africa, it’s mildly toxic to humans. From what we’re seeing today, the birds don’t seem very interested in it, either. But as we’ve already seen, the birds’ interest in different fruits can change greatly through the season. Near Helena, I’ve seen white-crowned sparrows eating nightshade berries in the fall. And Ser thinks they remember seeing song sparrows eating these fruits, as well.

Hints of mammals

Snowberries, mountain-ashes, red-osier dogwoods, nightshades – could there possibly be more types of fruit in Greenough Park? Then we pass by a small apple tree hanging over the trail. Yes, that’s right – a domestic apple in this semi-wild park. How did it get here? Did a bird plant it? A bear? A person? 

In any case, no fruits are left on it now. Some branches are broken out of the top, and we can see a series of deep scratches gouged in the smooth bark. 

We debate who the culprit might be. Could it be a raccoon? But we agree that the accumulation of signs – fruits gone, branches broken, and heavy claw marks – seems to point towards a bear.

The claw marks in the tree are another sign that far more is happening in this park than we’re likely to see in one morning. In fact, it’s likely that each day we’re here will bring us different stories.

Alysha Goheen lives near Greenough Park and comes here almost daily. Recently, she tells us, she was excited to see a pair of raccoons traveling along Rattlesnake Creek during the daylight. She’s seen raccoons here before – including, on one memorable night, a female with eight kits – but to see them during the day is something unusual.

“It’s really nice to be able to come out here daily throughout the season,” Alysha tells me.

Learning the stories of Greenough park

Today, we’ve seen neither raccoons nor their tracks. It seems that they’ve stayed denned up since last night’s fresh snowfall. Alysha’s story of the raccoon is yet another illustration of the benefits of a naturalist saunter like this. All of us have developed a more thorough connection with this park today because of each other’s perspectives and stories. From Alysha, we’ve learned of the neighborhood raccoons and their habits. Ser has brought us the stories of the American dippers and a thorough appreciation for the park’s diversity of fruiting shrubs and the creatures they support. Marilyn and Don have reminded us to wonder at the unfathomable, billion-year-old stories of the rocks we stand on. And Nate has shown us what may well be dipper tracks along the stream.

Even on a cold, wintry morning, the stories we can find when we saunter outside are endless. Next time, I’ll make sure to dress a bit more warmly. But although my fingers and toes are slightly stiff, I wouldn’t have wanted to miss this morning. Today I’ve gotten to connect a little bit more with the place where I’m living. I’ve made some new friends and gotten to see their passion and curiosity as, together, we celebrate the beginning of winter in Missoula. Next month, I hope to be back. What stories will we encounter in December? Maybe I’ll see you there.

Further reading

Lonn, J.D., McDonald, C., Sears, J.W., & Smith, L.N. (2010). Geologic map of the Missoula East 30′ x 60′ quadrangle, western Montana. Montana Bureau of Mines and Geology Open-File Report 593, 2 sheets, scale 1:100,000. Retrieved from https://mbmg.mtech.edu/mbmgcat/public/ListCitation.asp?pub_id=31350&

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