I wonder when the video was recorded. The mountain is currently closed to climbers due to recent volcanic activity. In fact, I wonder if the cache is still there!
I visited Mt. St. Helens in 2003, before I got into geocaching. Wish I had been doing it then! Anyway, after viewing the video, I was kind of surprised because I thought the area was now a national park, where geocaches are prohibited. But I checked the website and it's a volcanic national monument, under the jurisdiction of the US Forest Service -- in other words, a national forest, not a national park. So geocaches are OK!
That would be awsome to go after but If I do I'll make sure I have a pencil