Four years ago my wife bought me my first bonsai at Berkly Horticulture for $12.95. Somehow that little lime glow juniper is alive and kicking. In the time since we've "rescued" maybe two dozen spruces, firs, pines for between $5 and $50 from Home Depot, Lowes and WalMart, from 50% off to 80% off of the normal price. Heads up, November is the best time to buy fruit trees, they are on huge discounts.
Well, one of the natural progressions in the world of bonsai is to dig up trees from the wild and put those formerly wild trees into pots. Since we own a small plot of land, we have dug up trees on our property. However, as we have been out hiking this summer two new sources presented themselves.
First, four wheel drive roads. It's somewhat common for trees to start growing in between the two tire tracks, until they grow to around one foot tall, in which case they are cut or knocked down by the four wheel drive vehicles. So you end up with these small trees that have already had their tops knocked off, and frankly aren't wanted, they are a perfect target for a yamadori bonsai.
Second, ski runs are typically trimmed to make sure that nothing is very tall on them and even one foot of snow will cover everything. So again, they end up with these little trees that are less than a foot tall, and probably 10 years old, and look at least as tough as nails due to intentionally being covered with snow for six months of the year.
Now, standard disclaimer that on National Forest land you nearly always need a permit to harvest a tree (just like the ski resort has a permit to trim the trees) and on private land you will need the land owners permission to take trees as well. However, the upside to both of these locations is that as far as yamadori goes they are wildly accessible. You don't need to go off trail up a steep mountain to find a tree, you can actually just get out of your four wheel drive vehicle and dig up a tree in the middle of the dirt road.
Here is a directory that you can purchase with permit details for many national forests: https://humblebonsai.com/
Now a note on trees that you shouldn't bother trying to dig up, ones on the sides of cliffs. Every time I drive through Glenwood Canyon, or any other steep cliff and see the trees that are seemingly growing out of the rock, don't bother. I know Karate Kid 2 had that cool bonsai seen rappelling on the side of a cliff, but just don't bother. We had one of those on our property that we tried to dig up and the roots are nearly impossible to remove. You can get the trees out, but when you dig out the roots what happens is the tiny roots, which are the roots that actually transport water into the tree, get torn and then it's much more likely that the tree will die. Leave those trees to grow big on their rocky ledges, and enjoy looking at them in nature. Instead, opt for the trees that are actually possible to dig up and are likely candidates to be plowed up or cut down anyway.