ST. LOUIS — Scott Rupp flipped open the red spiral notebook he keeps as president of the St. Louis Amateur Hockey Hall of Fame and ran his index finger down the inside cover, along a column of surnames and birthdays that swells every year. Written in neat blue penmanship, they represent players who grew up in the area and have appeared in the N.H.L.

That list now numbers 22, and of that group, 14 skated this season, when Rupp would monitor their stats on his phone each night. At this late stage of the playoffs, with three teams left, his ritual does not last long. The only St. Louis player still active is Patrick Maroon, who foiled another local product, Dallas goalie Ben Bishop, to score the winning goal in double overtime of Game 7 last round — for none other than the hometown Blues.

“This is beyond what I ever thought would happen,” said Scott Sanderson, a longtime pillar in the amateur hockey community.

The pipeline of American hockey snaking from Massachusetts west into Michigan and Minnesota has meandered south, following the Mississippi River into an area thronging with tradition but that until recently had not produced the talent to match the fervor. A decades-long endeavor — rinks sprouting, participation swelling, Blues alumni staying in town to coach — culminated in 2016, when five St. Louis-bred players were drafted in the first round, or five more than ever before.