The Tale of Black Diamond Pool
I am very deep in my Yellowstone National Park/geyser hyperfixation, so today I am going to tell you a story about one of my favorite geyser basins.
It’s called Biscuit Basin, located not far from Old Faithful in Yellowstone’s Upper Geyser Basin.
It got its name from sinter deposits that looked like biscuits, found along the crater of one of the most stunning thermal features in the park – Sapphire Pool. (Most of the biscuits, sadly, were broken after an earthquake in 1959 caused the pool to erupt.)
(yes, those shadows are me and Real Life Romance Option being terribly cute and romantic about a thermal feature)
Biscuit is also home to some very spunky and personable geysers, Jewel (left) and Shell (right):
And some really fabulous bacterial mats:
However my favorite thermal feature is this gorgeous pool:
Or. Was.
...because in 2024 it blew up. You may have heard about it. If you haven’t, there is some incredible footage of it. No one was hurt in the explosion, thankfully, and it’s an awesome thing to see.
Now, here’s where it gets weird. For me.
The thermal feature that exploded is named Black Diamond Pool. There's just one problem. According to just about every map you can find of the basin, Black Diamond is located in the spot occupied by my favorite pool. But according to all my photographs over multiple visits, the placard for that feature stated it was Wall Pool:
I was…perplexed by this. That stretch of the boardwalk, which is immediately across a bridge from the parking lot, does contain multiple thermal features. Including Black Opal Spring, which is immediately to the right if you are standing on the boardwalk:
I always photograph placards when I shoot thermal features to keep my sanity, but on multiple trips shooting this basin, I never photographed a placard for Black Diamond Pool. Only Wall and Black Opal. But no article I could find even mentioned Wall Pool. So what the hell was happening?! What blew up?! The photos of Black Diamond post-explosion looked nothing like my gorgeous turquoise marvel. The indicator arrow of this map pointed at the far corner of the pool:
...which according to my photos was this feature:
A much smaller, moodier pool at the back of my favorite show stopper.
So… was that Black Diamond? Had it exploded and muddied my beloved Wall Pool? WHY WAS NO ONE MENTIONING ONE OF THE MOST GORGEOUS THERMAL POOLS IN YELLOWSTONE. I was going a little insane about it.
FINALLY. After much googling, asking tour guides, etc., I found this article by Janet Jones, who is now one of my favorite people and has no idea she has saved me from being gaslit by a thermal feature. Which includes a map of all three thermal features along that boardwalk:
And includes this observation:
“In 2011, the NPS workers inadvertently swapped the signs for Wall Pool and Black Diamond Pool, so some reports of eruptions that have come in since then may be listed as Wall Pool but were likely Black Diamond.”
THEY SWITCHED THE DAMN SIGNS. FIFTEEN YEARS AGO. AND NEVER SWITCHED THEM BACK.
All this time I have been in love with a pool by the wrong name.
Biscuit Basin has been closed since the July 2024 explosion, with no word on when/if it might be accessible to the public again. A web cam has been set up on the boardwalk along with monitoring equipment. Most recently, in December 2025, another minor eruption was observed and officially described by the USGS as “kablooey!”
So, sadly, the answer is that my favorite pool in Biscuit is now a muddy disaster area I can't visit. Here’s hoping one day that changes and I get to go back and say hi to my thermal bestie, Wall Black Diamond. She’s beautiful no matter what her color. Or her name.
