I remember one time about 35 years ago me and my buddy Dave was enjoying a day of heavy duty fucking off down in the lower Mother Lode, and headed south past Hornitos, turning on to Old Toll Road which was a narrow, twisting (are you ready for this?) old toll road from the 1850s linking mining camps to the area around Mariposa.
We had pulled over to roll a joint and so Dave could take a piss and he hollered at me to come check something out. I got out of the truck and looked to where he was pointing, and down in the valley below us, it looked like the ground was moving. Right about that time, a fucking wave of Monarch butterflies crested the hill and swept up over the road, my truck, and us. There were millions of them and I'm not exaggerating - they were so thick that with me and Dave standing 30 feet apart, we couldn't see each other. We could actually hear those little fuckers as they were moving the air around with their wings, sounded like a whisper.
We enjoyed it for a few minutes and left. We had to pull over in Mariposa and hunt for a car wash because I had butterfly goo all over, and I do mean all over my poor truck.
What was worse was after we headed north towards home, we got about halfway between Mariposa and Coulterville on Highway 49 and my fucking truck started overheating. You guessed it, my radiator was covered in butterflies and not allowing any air passage. What was bad is there's no towns between Mariposa and Coulterville where we could've cleaned them out with water enough to make it home. When we finally made it home hours and hours later because we had to keep stopping to let the engine cool, I had to pull the radiator completely out and spray the fuck out of it just to get the mess out between the cooling fins and tubes.
We marked that day and went back on that some day every year for the next 5 or 6 years hoping to see it again, but that was the only time we got lucky.