Lois was trapped here. She left that clue.
3 seconds sound clip from Superman (1948) - Blast In The Depths (Chapter 12).
You can hear this line at 00:12:23.209 in the Blu-ray version of the episode.
Quote context
[...]
- A mining engineer's guide. It may help me find a clue.
- Here's something. A list of mines and mining locations.
- A location of a mine at Question Crossing.
- But those scratches mean something.
- Lois was trapped here. She left that clue.
- How do we know they took her there?
- That's what we've got to find out.
- Yeah, but how are we gonna...? Hey, wait for me.
- No chance to get in that way.
- There's another tunnel further along. We can get to it under cover of brush.
- You go in that way, and I'll go in here, but walk slowly.
[...]