PLACER RIVER VALLEY -- Not far off the road in Alaska can be found the agonies that remind one of the simple things in life for which to be thankful, like firm ground.

Firm ground might not seem like much of a luxury to most people. Much of the USA -- from the wheat fields of the Dakotas to the arid hills of southern California -- is full of it, and firm ground is everywhere in American cities.

The streets and sidewalks are paved in unbending concrete and asphalt, the grass patches between underlain with firm dirt. Even in the small towns of the nation, where concrete and asphalt are lacking, there are alleys of good gravel, and paths of rock or wood chips.

Not in the far north.

Spend a day or days in some of the gnarlier terrain of Alaska, and you begin to yearn for such surfaces.

Oh but for some concrete steps across the loose and shifting scree of the Chugach Mountains, where for every step forward you pay with a half-step back-slide. Please for a boardwalk across those miles-long fields of tussocks too awkwardly spaced to walk atop, and full of water and ankle-twisting nooks between.

And these are among the better terrains.

When it comes to abusing the planet's only fully bipedal species, none of these surfaces can compare to the sponge bog of Alaska swamps. I have seen sponge bog elsewhere. As a kid growing up in the flatlands of Minnesota, I early on encountered floating mats of vegetation over water around lakes, and a few sponge bogs. None of these though, ran on for miles and miles and miles.

Maybe once they did, before white men arrived on the prairie and in the forests along the Great Lakes to clear and drain the land for agriculture. But by the time I was born, there were farm fields and dirt roads all over that country, and if you did have to fight your way across bog it wasn't for far. Alaska is different that way.

From the middle of the North Slope west around the tip of Alaska and then south along the Yukon-Kuskokwim Delta all the way down to the Kenai Peinsula, Alaska is full of swamp. From the saltwater end of this valley at the head of Turnagain Arm, you can head south from the Seward Highway and go in a straight line for almost 10 miles -- if the rivers are low enough to cross -- with little but flooded bog of various sorts underfoot nearly the whole way.

Why would one do this?

To kill a silly little duck, of course, to savor the experience if you are a bit masochistic, and to develop a rich and true understanding of the luxury of firm ground.

If you have never thought of firm ground as a luxury, you have never been to that place where you decide it is easier to detour into a dense thicket of alders and fight your way for every inch than to endure another foot of forward motion on nature's unforgiving stair machine. Anyone who has been to a modern athletic club knows what a stair machine looks like and probably how it works. The machine has a couple paddles on which you put your feet. When you weight one paddle, you push it down. The other paddle then goes up. You get your exercise by climbing a set of endless stairs.

The bogs of the Placer are like this, only worse. The stair machine requires a step up of 8 inches to a foot. Sometimes in the marshes here, the step is two feet or more. In the very worst places, you can find yourself standing in water crotch deep atop a bed of vegetation that had been floating on the surface of water. You will be looking ahead at a bed of vegetation still floating on the surface of water and thinking about how you will need to get your foot up high enough to drive the vegetation back down again to move forward.