The mystery continues: What is blocking tunneling machine under Seattle

Short form: a tunnel-borer working to make an automotive tunnel 60 feet or so under Seattle ran into something it can’t bore through. Boring, reasonable explanations include:

1) A really hard rock (granite, iron ore, etc)

2) Something man-made, like a big chunk of iron or steel. It’s boring through a region of “fill”, so it could be anything, including concrete.

But… yawn. What else could it be? A naquidah deposit? An actual Stargate? A Cybertronian Ark? Dragons? A Martian spaceship full of dead telepathic grasshoppers? A Martian war machine?

Or, could it possibly be…

Another good possibility: since this project is to create a tunnel 1.7 miles long but costs $4 *BILLION*, perhaps it’s just a whole lot of bags of pennies.