Subject: the most memorable or significant geological event that you’ve directly experienced.
Excluding direct weather events, e.g., a tornado, dust storms (including a day-long dust storm waiting for the Space Shuttle to land at White Sands Missile Range), dust devils, and the remnants of a hurricane over the Eagle Mts.,...the most memorable geological event in my memory was the result of a weather event that happened a few miles away - A flash flood in New Mexico.
It was probably 1985, my wife and I went from El Paso to Hillsboro, New Mexico to visit a Labor Day weekend outdoor antique festival. During a previous year, I had a table selling beer collectibles ("breweriana") during one of the festivals and made a small profit. The first few outdoor antique festivals I attended were either on Memorial Day weekend or Labor Day weekend, I might have done the Memorial Day, it has been so long, I don't specifically remember.
At some point, the organizers decided to consolidate to the Labor Day weekend, to coincide with the Aspencade, enjoyed by bikers - you know the Harley-type bikers. There was one bar in town, when it was taken over by bikers, it made for some interesting encounters. The bikers were usually well-behaved during the daytime, as there was a healthy contingent of New Mexico State Police in the streets.
Anyway, after enjoying the festival and navigating the biker-filled bar for a beer, we decided to leave. Afternoon and evening summer time thunderstorms are not unusual in the area. I don't recall it raining in the town that day, but we were aware of storms in the mountains to the north and east of Hillsboro. After weaving through the mountains, we approached the last arroyo crossing before a long flat area that led to I-25. The arroyo was probably 4 or 5 miles east of Hillsboro.
Traffic began to stop and to our left, we could see that parallel to the road, the arroyo was filled with a "healthy" flash flood. As it was obvious that we weren't going anywhere for a while, I stopped the car and walked a couple of hundred yards down the road to get a better look at the flooded road and the upstream area. [As there weren't a huge number of cars, it was likely that the flood had only covered the road for maybe 15 to 20 minutes.] While watching, I observed one or two boulders - probably 3 feet in diameter - slowly tumbling in the muddy water. They didn't move far, but they did move. After a few minutes of "wow" - but lacking a camera - I decided to walk back to the car.
My wife and I had three choices: 1) Wait on the road until the flood subsided and the road was cleared; 2) Go back to Hillsboro and take the southern road from town - several tens of miles extra driving to get to I-25 or I-10 to the south; or 3) Or go back to the bar and have another beer or two with the bikers and then try the same road an hour or two later. We chose #3. By then, the road crossing had been cleaned of gravel and cobbles and we continued on our way, back to El Paso.
My uncle in Phoenix had warned me of flash floods well before I moved to El Paso, so if we had been there while the leading edge of the flood was within sight, but upstream from the road crossing, knowing the acceleration qualities of a Chevy Chevette, I probably would have opted to test the brakes and remain on the west bank of the arroyo, i.e., not try to "beat it out".