You will need to change the numbers and timing to fit. Also, I'm not too happy with how the grains get there.
100 000 000 BC
Mount WannaMakaLotaBrew started off life as a crack in the Earth's crust with a silver spoon (er...ore) in it's mouth.
Being born near the beach (and creating the beach) this allowed layers sand to be mixed in with layers of silver ore (antibiotic)
As time went on, plant/animal life started to appear.
Every 100 years or so, Mount WannaMakaLotaBrew turned them all living matter into a nice layer of charcoal (other filtering)
1 000 000 BC
Mount WannaMakaLotaBrew decided to get some rest but had a lot of magma left to get rid of first.
For years, Mount WannaMakaLotaBrew gave the lava in a slow steady fasion.
In the process, lava tubes formed.
When all was done, Mount WannaMakaLotaBrew rolled over causing the lava tubes to now be at steep angles.
5 000 BC
Princess Buzzbuzz Bzzz (a wild queen honey bee) decided to leave her hive and start her own hive.
After days of searching, she ran across a nice little cave system. It was long, dark, and stayed warm in the winter.
She had found one of the lava tubes of Mount WannMakaLotaBrew.
She picked a spot near the location where snow melt was starting to be collected. This collection would grow into underground lake, and provided the hive of Princess Buzzbuzz Bzzz a source of clean fresh water and cool air during the summer, and the heat from the lava tube's bottom provided the warmth through the winter.
Her hive would thrive.
As the years go on, Mount WannaMakaLotaBrew tossed and turned. In the process, parts of the honey collected by the hive of Princess Buzzbuzz Bzzz broke off and fell down the lava tube.
After eons, the bottom of the lava tube had collected a ton of honey. Honey that is as ancient as that found in Egyptian tombs and just as well preserved.
A tribe of Native Americans found a cave system with a bottomless pit.
To appease the god of Mount WannaMakaLotaBrew, they would sacrifice a 100 pounds (adjust numbers to make sense) of grain down this bottomless pit.
Every now and then, Mount WannMakaLotaBrew required more sacrifice and showed his dissatisfaction with an earthquake.
A former brewmaster from the Yuengling family wanted to start his own brewing company out west.
While on the Oragon Trail, he spotted some Native Americans near Mount WannaMakaLotaBrew.
In preparation for an ambush, he hid a barrel of brewers yeast in a cave close to a pit. (the same bottomless pit)
He died of dysentery shortly after.
Due to global warming, the top of Mount WannaMakaLotaBrew became the perfect spot for growing hops.
The Portland Brewing company had a high demand for Oregon hops. A lot of farmer land appeared, adding many silos of hops to the top of Mount WanaMakaLotaBrew.
Near Future + 1 day
Mount WannaMakaLotaBrew was beginning to wake up.
An earthquake caused a fissure near the top. This fissure swallowed some of the silos of hops down and their contents to the bottomless pit (lava tube).
Additionally, the abandoned barrel of brewer's yeast from 1800's fell into the pit.
The underground lake drained into the pit also.
Mount WannaMakaLotaBrew had heated up the bottom of this particular lava tube for the correct temperature for brewing beer.
(Optionally) Mount WannMakaLotaBrew heated up the lava tube that the hops fell down high enough to slightly toast them.
Near Future + 3 months
Winter at the top of Mount WannaMakaLotaBrew has come and gone.
The snowmelt found a new route. This new route leads the water to the bottomless pit that contains the beer mash.
This allowed the millions of gallons of (now beer) liquid to reach a particular point where it can drain to a lower elevation (like a toilet flush)
As it drains, it passes through sand (filter), silver ore (antibiotic), charcoal (poison filter), and more sand (extra filtering) making the brew safe to drink as it gushes out into a nearby reservoir.