Good question considering the fallen rocks all over the place and the general bowl shape of the bluffs around the lake. It does look like some old quarries I’ve seen. In this case however, it’s not an old quarry but all natural. The bowl shape you see was cut into the bluffs by ancient rivers and sealed up by glaciers over 10,000 years ago. All that rock you see, cracked, shattered and fell due to high winds, moisture and sub-zero temperatures many eons ago. Those boulder fields, sometimes called scree or talus, certainly look “blown up” by dynamite, but they are completely natural. And yes, sometimes big boulders do still come tumbling down, but very rarely.
Just and FYI, there were 2 private quarries in the park many years ago. Both were on separate sections of the park’s east bluff and are pretty much indistinguishable from the natural talus fields around them today unless you know where to look.