Jessica's requested meme, from One Continuous Fight: The Retreat from Gettysburg, by Eric Wittenberg et al:

Imagine a long column of cavalry winding its way up the mountain side, on a road dug out of the mountain side, which sloped at an angle of thirty degrees just wide enough for four horses to march abreast - on one side a deep abyss and on the other an impassable barrier, in the shape of a steep embankment; the hour ten o'clock at night, a drizzling rain falling, the sky overcast, and so dark as literally not to be able to see one's own hand if placed within a foot of the organs of vision; the whole command, both men and animals, worn out with fatigue and loss of sleep...

It is, itself, a quote from a New York Times correspondent's description of Custer's brigade riding towards what would be a successful ambush of a retreating Confederate wagon train in Monterrey Pass over South Mountain after Gettysburg.