River crossings are one of the most dangerous activities you can do on a long distance hike, so (needless to say) it's good to be prepared. Ned Tibbits is a wilderness skills instructor for Mountain Education, Inc. and has nearly 50 years of experience as a wilderness ranger, paramedic, ski patrolman, and much more. 

Here, in an excerpt from his upcoming book, Ned covers the basics on river crossings, timing on entering the Sierra, and different scenarios to keep in mind.  

Sierra Creek Crossing, Introduction:
There are two major environmental dangers that can, and have, killed Pacific Crest Trail (PCT) thru-hikers while going through the Sierra (note, I did not include all the minor ones!)

1. A slip-and-fall on steep snow resulting in an out-of-control tumble down the mountainside resulting in a crash into a tree, boulder, creek, lake, or to just go over a cliff and die on impact, and
2. Getting knocked over by raging waters during a precarious creek crossing.

This chapter is going to address the second one and give you a safety advantage in dealing with them.
What Is A Creek Crossing?
“Oh, come on, Ned! Aren’t you being a bit mellow dramatic, here? Near my home, the National Park either had bridges over the creeks or they were slow and shallow enough to walk right on through.”

Creek crossings where you don’t get wet in the process, which I’ll refer to as “dry crossings,” are accomplished by walking over man-made, rigid wooden or steel bridges, on cable-suspension bridges, along the tops of logs (or collection of smaller branches or logs) that have just so happened to have fallen over the creek near the summer trail’s crossing location, or by hopping from dry-topped rock to dry-topped rock right across the creek, itself. (More on stepping on wet rocks later).

Creek crossings where you do get wet in the process, which I’ll refer to as “wet crossings,” are accomplished by actually getting into the water and finding a path across where, 

1. the slope isn’t so steep that erosion over time has exposed rocks on the bottom that are too big to go around or over, so angular that they may cut up your feet, or too numerous to find solid footing, 
2. the flow rate isn’t too strong so as to push you over or suddenly move your feet or poles so you can’t make and maintain solid foot and pole placements, 
3. the depth isn’t too deep (even in the deeper, main channel) so as to rise above your legs and push against your pelvis or torso (the broader, more easily pushed parts of your body),
4. there are no dangers downstream, should you fall in and get swept away, and 
5. access into and out of the creek bed is easy.

Since a fair amount of the PCT is wilderness, where no sign of man is allowed, bridges are not commonplace, so hikers have to find routes over or wade through creeks to get where they’re going. Creeks come in all shapes and sizes and some are easier to cross than others during the PCT thru-hiking season of March to October. The idea is to not get wet, since getting wet is not good when walking over snow or in very cold weather, so I will discuss how to do that, first, then how to wade through them safely.

Creek crossings become dangerous when two factors combine, water volume and speed. Volume is experienced as the depth of the creek and the speed of the water is created by the steepness of the mountain side and narrowness of the valley. Creek volumes increase when there is more snow to melt into them, say when you cross a creek that has miles of tributaries above you (a low elevation crossing). Creek speeds or flow rates increase the steeper the grade becomes combined with a narrowing of the valley.

The Practical Side:
So, when you’re looking at your topo map at dinner along the trail, looking at the route ahead for navigational landmarks and potential dangers, (something all of you should do when the trail is buried under snow and there is no boot track to follow), find all of the creeks you’ll have to cross and note both of the details, above, how steep the terrain is there (as shown by the closeness of the contour lines in the area) and how many miles it is from there to the creek’s headwaters.

Any creek crossing that you find in a steep and narrow drainage that is fed by miles of tributaries into high, alpine bowls above you (look at the PCT crossing of Rancheria Creek in Kerrick Canyon in Yosemite National Park north of Tuolumne Meadows) is going to be a challenge worthy of preparation or avoidance. 

However, creek crossings done in flat meadows are much safer. More on this, later, too.

“Ok, Ned. I get the idea. If I want to thru-hike the PCT north-bound up the Sierra, I’m going to have to cross some dangerous creeks. Can’t they be avoided? Are they nasty all the time?”

When Are Creek Crossings The Most Dangerous?

The creek flow rates and volumes are the most dangerous during the first half or two-thirds of the total snowpack melting period. This period of time is called, the “thaw.” 

On average, the thaw starts in late May or early June. It is identified when nighttime temperatures rise above freezing and stay there while daytime temps, also, increase dramatically. This temperature change no longer re-freezes the snowpack at night and it begins to start melting around the clock, creeks begin filling with water, the snowpack no longer supports your weight so you fall into it (something we call “postholing”), and water starts flowing everywhere, even transforming trails into little creeks. 

In general, and to give you a time frame to remember to avoid, you do not want to be in the High Sierra during the first two-thirds of the total thaw. For the most part, that will be June and, maybe, into July, depending on how much snow needs to melt off the land. 

“How Long Does This Risk Last?”

When there is a lot of snow in the Sierra to melt off, say after a heavy winter, the thaw will last longer than if there was less (in general), say after a mild or light winter. The approximate numbers that follow will give you an idea:

Drought winter = 4 weeks of questionable creek crossing risk (all of June)
Light winter = 4-5 weeks (June and the first week of July)
“Normal winter” = 6 weeks (June and half of July)
Heavy winter = 6-10 weeks (June, July, and maybe half of August)

The Practical Side:
“What can I expect the high Sierra to look like before and during the thaw?”

What you see when you get there, whether that’s where the snowline is first encountered, how deep the pack is at PCT/JMT “cruising altitude” (say, 11,200 feet), or how much water is in the creeks, depends on how severe the winter was preceding and the month you are there. Let’s start with after a “normal” winter (thaw starting June 1st):

“Normal” May: 
Usually presents itself with the most stable snowpack and best snow-hiking conditions and situations:

- the snowline may be at 9500 feet on south-facing exposures (called “aspects”) and even lower and deeper on north-facing ones,
- not a whole lot of powder snow falls during this month to cause avalanches and the pack, itself, is quite frozen and not moving (this varies from year to year), 
- the surface of the snow is quite wind-smoothed and cold enough to support your weight without snowshoes making for easy walking on inclined “ramps” everywhere,
- there will probably not be a "boot track" to follow over the snow, so, accurate navigation is vital,
- there might be enough feet of snow to cover all obstacles on the ground (logs, boulders, bushes, creeks, and little trees) making for easy, unobstructed walking everywhere, 
- hazardous, over-hanging cornices are receding and less of an avalanche-triggering threat to hikers,
- most creeks have a thick enough covering of frozen snow to make secure, reliable (always test them first!) “snow-bridges” across them for easy passage,
- the weather is beginning to warm up, but the nights are still well below freezing (maybe down into the teens; this is good as it re-freezes the snowpack nightly) and daytime temps only rise up to the 40s, and
- over-snow route-finding or navigation is easily accomplished because everything is covered up and you can walk most anywhere your skills allow.

“Normal” June:
- the snowline may rise up to 10,500 on southerly aspects, but remain down at 9,500 on the northerly sides of things,
- very few new powder storms arrive in June, but 3-foot snow storms have arrived in the past causing avalanches, buried hikers, and hypothermic conditions, 
- the surface of the snow is too soft to hold your weight after mid-morning causing postholing to begin (“suncups,” also, start appearing in the surface making for difficult progress),
- there will probably be a boot track to follow over the snow, but it may not go where you want,
- as the snowpack thins, more buried obstacles appear reducing the number of safe route selections,
- cornices melt back or fall along the northern and easterly ridges making for safer passage over them,
- snow-bridges start thinning, making for dangerous crossing assessments, and falling into creeks as the weather warms and winds pick up, marking the beginning of wet crossings, 
- creek levels rise from inches to several feet deep, flow rates soar, and meadows flood (waterfalls are everywhere) making most crossings unsafe for animals, small people, and the ill-prepared,
- nighttime temps may not drop lower than 40-degrees while daytime temps climb up into the 70s.

“Normal” July:
- snowline may rise up to 11,500 or higher on southerly aspects, yet remain down at 10,500 on the northern ones; snow recedes up onto the steeper slopes of the passes,
- days are usually filled with warm to hot springtime sunshine and temperatures causing a rise in the chances of local lightning and thunderstorms due to the higher humidity from the melting snow,
- boot tracks start appearing on the remaining snow-covered trails as more and more summer hikers enter the Sierra causing flatter, firmer, and safer in-track foot placements in the more-packed snow, though postholing persists off-track,
- Creek depths and flow rates begin to recede the latter part of the month as the snowpack diminishes, but are still hazardous to small people and animals,

Knowing this, and establishing through your own winter and springtime weather and remote snowpack monitoring the “normalness” of the season’s snowfall and thaw, you can foresee the snowpack and creek levels that you’ll have to deal with once there. 

“Drought” or “heavy” winters will change what you see and when compared to the “normal.” For example,

- a low or “drought” winter may cause July conditions to be experienced in June, and 
- after a “heavy” winter, early June conditions may continue to be experienced even into August!

Thaw Intensity:
Also, the speed at which the snowpack thaws is heavily influenced by weather factors like constant sunny and warm days, additional snow or rain storms, simple cloud cover, wind, and humidity. 

- Events that will prolong the melt or extend the thaw’s duration are cold, wet air masses, additional snow, and cloud cover. 
- Events that will accelerate the melt and shorten the thaw’s duration are clear, hot days, fair weather winds, and rain storms.

You have decided to start your NoBo hike on April 25th. At the time you left home, the Sierra snowpack was at 100 percent of normal according to the California Department of Water Resources (DWR) and small snow storms were still expected to roll into the southern Sierra according to NOAA forecasters. During the 4-6 weeks that it takes most hikers to reach Kennedy Meadows (south) (KMS), you find out at various town resupply visits along the way that the storms didn’t amount to much, the thaw started the last week of May, and the weather over the Sierra has been intensely hot and windy.

You expect to arrive at Chicken Spring Lake on Cottonwood Pass around mid-June. Will you experience typical, better, or worse mid-June snow and creek conditions? Will your estimation change the safety gear that you decide to take with you into the Sierra from KMS?

Intro Synopsis:
1. North-bound (NoBo) PCT thru-hikers may encounter two historically fatal environmental conditions as they snow-hike through the Sierra, steep and slippery snow and whitewater creek crossings.
2. Creeks can be crossed via two general choices, wet routes and dry ones (preferred). 
3. Factors that contribute to safer crossings are the grade and width of the crossing location, the size of the rocks and obstacles making up the creek bottom, the speed and depth of the water, the presence of downstream dangers, and ease of entry and exit.
4. The start of the thaw marks the onset of dangerous creek crossings which usually doesn’t diminish to manageable levels of safety for weeks to months depending on its intensity and the depth of the snowpack.
5. May, June, and July are the usual NoBo PCT thru-hiker months in the Sierra and each has its own expected benefits and hazards depending on the intensity of the preceding winter and the following thaw.

So, you can, now, see that the risk of having to deal with nasty creek crossings on a thru-hike of the PCT is a consequence of the severity or depth of the winter’s snowpack and the time of year you are there! Now that you know what one is, where the worst ones might be encountered, the two main ways to cross them, and how the risk of doing so varies with the depth of the snowpack, thaw intensity, elevation, distance to headwaters, and month, let’s move on to planning for them!

(c) 2021 Mountain Education, Inc.

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Ned Tibbits, PCT Class of 1974
You can reach out to Ned on Facebook and you can learn more about wilderness skills and safety via Mountain Education, Inc.