Jason Chandler was a busy man. He had a secret organisation to oversee, and that was while he was working on his inventions.
So to recieve correspondence from an old friend was entirely expected, and yet in another way, unexpected. Expected in that it was an old friend, and a member of this organisation. Unexpected in regards to the letter's contents.
Barnabas T. Bullion, now the sole owner of the Big Thunder Mining Company, was having problems over at Big Thunder Mountain. Jason was familiar with the first problem - he had been there and very nealy lost his life. He warned Barney about continuing his prospecting endeavours at the mountain, but had been ignored.
Now there had been a second incident just like it.
Jason knew it was time - overdue, in fact - for Barney to give up mining at Big Thunder Mountain, but how on earth was he going to get through to his old friend?
Fortunately, he knew exactly who he needed to talk with; his dear friend Vidalia. Or as she was more commonly known, Madame Zarkhov. The fortune teller and proprietor of the Museum of the Weird.
If he couldn't get through to Barney, perhaps she could.
This is based on the letter in the queue for Big Thunder Mountain where Barnabas T. Bullion is warned against prospecting at the mountain by both Jason Chandler and Madame Zarkhov - but they aren't listened to and Bullion continues prospecting.
From this line in his letter;
"I did warn you that you were prospecting at your own peril when I sold you the drilling machine"
it can be inferred Chandler had warned Bullion against prospecting in the past as well.
Per Chandler's original backstory, he's an inventor who supplied Bullion with his mining equipment and narrowly survived a cave-in.
Bullion being the sole owner of the Big Thunder Mining Company - in Disney lore there's been two owners. Bullion and Henry Ravenswood. I'm going off the theory that they were co-owners and when Ravenswood died, Bullion became sole owner.