A collection of 1948 baseball cards discovered in an attic in unopened packs, and in exceptional condition, are part of a trove of sports trading cards that an auction house said could fetch nearly $1 million.

For Brian Drent, president of the auction house, the Mile High Card Company, seeing the find up close was an exhilarating, romanticized part of the chase — a bit like Indiana Jones in the beginning of “Raiders of the Lost Ark,” but minus the rolling giant boulder.

“Every single day when I go to work, I have this thought that something like this can happen,” Mr. Drent said on Monday. “We’ve had great days, not every day and not to this level.”

What set his heart racing started with a phone call that was answered by the company’s head writer, Mitch Rosenberg, a few weeks ago at its offices in Castle Rock, Colo.