It's not uncommon to see talented racers from the same geographical area at the same time. While it would appear to be a statistical anomaly, quite often, talented athletes go all the way from battling at local races to the national stage. If you look back to the '80s, the riders from the "El Cajon Zone" produced multiple national champions. Before that, both Chuck Sun and Rick Burgett climbed from the pacific northwest to battle on the national circuit. Almost every star in the sport has a childhood rival who pushed them to a very high level.
(Garrett Marchbanks became the first rider in modern racing to win a Supercross)
The latest geographical area to produce talent is Utah. Garrett Marchbanks became the first rider since Bob Plumb to win a Supercross (I can't find any verification of Bob's 500cc support class win in the '70s, but my dad holds firm that he did in fact win). Currently, Marchbanks and Pierce Brown are both on the verge of superstardom. Motocross success is new for Utah; kids who live in Utah have been passed over throughout most of the 80s and 90s. It's challenging to keep up with riders who can practice year-round, in Utah snow prevents racing or practicing for at least three months out of the year.
(I can't verify it, but have been told Bob Plumb won a 500cc support class in Supercross)
It's no surprise that these kids grew up racing each other and used each other as measuring sticks. They draw confidence from each other's success. I can promise you when Brown saw Marchbanks win at Daytona; his sixth-place went from an excellent finish to a steppingstone finish. Using a baseball example, two Utah kids on my very first little league team, Brandon Duckworth and Ryan Jensen both went on to play in the Majors. They mirrored each other, and even though they didn't train together, they did feed off each other's performances. Eventually they both hit the Major leagues within a year of each other, any success achieved would automatically transfer confidence for the other.
(Pierce Brown could be a superstar in the making, interview link at bottom of page)
Don't expect Brown and Marchbanks to be the last riders from Utah to hit the highest level of Motocross and Supercross. While some areas are struggling to find places to ride, Utah has embraced the sport. Former Governor Jon Huntsman Jr has a passion for motorcycles, and the Utah Sports Commission has titled Utah, "The State of Sport." Unlike many areas in the country Utah has multiple successful racing series; RMX, Wild West Nationals, and USRA. If you want to find the stars of tomorrow, no need to look past Utah, the state will be producing quite a bit of talent in the next few years.
(Not many politicians embrace Supercross, but former Governor of Utah Jon Huntsman Jr. loves the sport)