This looks like aspen root sprouts. Was an aspen cut down nearby recently?

Not that I’m aware of but these seedlings are everywhere much like maple trees.

Actually we have one tall tree that looks like a birch but perhaps this is an Aspen

Aspen root suckers

Yes, aspen are colony plants and will send up root sprouts regardless. IME they tend to be more dense when there has been an injury either to the original tree or the roots. IME these are rarely seedlings but are almost always suckers/sprouts from the roots of an already existing plant. They are colonial, so in an aspen grove, typically all the trees are genetically identical because they are all connected to the same set of roots.

Very interesting, thank you for the insight! It’s amazing how many plants there are and how different they behave. Cheers!

A section of the involved rootstock is even visible in your photo. And there are entire mountainsides covered with groves of interconnected aspen trees that have been discovered through DNA sampling to consist of a single, ancient clone. In other words the whole enormous patch in each such instance is one genetic individual. So, yes, this species suckers a lot.

Just dug it up and you were right, what a root system