That is certainly one, very long train platform!  And if you look closely, there seems to be a train, or trains, wrapping around the far end of the platform. How odd!

It’s unclear exactly what is going on, unless the railroad brought in a 19^th century wood-burning steam engine and its boiler exploded.  Diesel engines can catch fire and may explode in certain conditions (aside from a crash). Since this is an adventure strip, I’m guessing this was either sabotage or an explosion of chemicals illegally being transported on the train.

Anyway, Mark and Happy are not train inspectors, nor do they presumably have any experience in crash investigations or forensic analysis. But who is going to tell that to Happy Trail, one really pissed off dude missing his father-son fishing trip!?