I have been told how the Cairn Junction cairn came about.
No one was lost. It was built as a marker on the day that the Pitch Bypass was found. This was explored from Cairn Junction upwards and someone just thought that something was needed to show the new way out. It seems everyone that day entered via the pitch and exited via the Pitch Bypass.
Not sure who did the construction but this was very early in the cave's exploration so there would have been mainly Morgannwg C C members involved, along with a few others.