That plaque was installed on a ledge near the top of the second pitch of the Becky route by myself and several friends in 1971. The plaque was a memorial to our friend, Marc Emerson, who died trying to free the "Northwinds" route on Castle rock in 1970.
Instead of tying in directly to his harness (1" webbing wrapped several times around his waist) he had clipped a biner to his harness and clipped into that with a figure 8 knot which came unclipped after he had fallen and was being lowered past an overhang. He fell 120' to the ground. He was (we were) 16 years old at the time.
Of all of us that later became dirtbag derelict climbers of the 70's venturing around the world persuing our climbing needs, Marc was by far the most normal with the brightest future ahead of him.
Let this be a lesson about knot safety and rope management. Although I came extremely close many times in the next 30 years of climbing, to dying an ignominious death in the mountains, I never forgot the lesson about tying in directly to my harness.