It used to be said that you could go down a coal mine in the north-east of England and surface with a team of top-class footballers.
These days, the same can be said about the quarries of northern Spain. A "quarry" is the name given to the youth academy of a Spanish football club - they are proving to be rich in nuggets of footballing gold.
I commentated on the Basque derby last weekend when an incredible 36 of the 47 players in the match-day squads of Athletic Bilbao and Real Sociedad came from the region. It's well known that Athletic demand a player must be of Basque heritage to play for the club. Remarkably, their opponents boasted more graduates from their academy on the full team-sheet.
While Athletic raid local clubs to buy the best talent or lure players back to the region with a promise of premium wages, La Real catch the kids young and have the most prolific academy in Europe. It's quite a contrast. One club scours the country for expensive talent with roots from the area; the other scours the local playing fields and grass roots football.
Both clubs are thriving with players bursting with local pride. The Lions of Bilbao roared into third position by beating Real Sociedad whose coach Imanol Alguacil described them as the toughest opponents he's faced this season. That's a lot of love between two clubs who are historical rivals.
As Athletic Club head above Barcelona, La Real are on an adventure of their own. Unbeaten in the Champions League, they have a glitzy match-up with Paris Saint Germain next month. Although Real Sociedad don't restrict the team to Basques only like Athletic, they always have more local players than outsiders.
I once asked David Moyes why he'd chosen a reserve striker instead of the in-form Willian José. He explained that he needed six Basques and playing José, a Brazilian, would have upset the balance.
Moyes was a manager imported to San Sebastian, the capital of the Gipuzkoa region of Spain. This is an area which has exported some of the most successful coaches around Europe.
It's remarkable that Andoni Iraola, Unai Emery, Julen Lopetegui, Mikel Arteta and Xabi Alonso are all from the same area and have been flying the flag in foreign leagues.
Alguacil is the brains behind the Real Sociedad success story having played for the club and worked his way from academy coach to the first-team boss. Jagoba Arrasate led Osasuna to the Spanish Cup final last season – he's from the next province.
The managers of Arsenal, Aston Villa, Bournemouth, Borussia Dortmund, are spreading the word. They all have their own individual quirks, but all come from the same region and share the same qualities.
It's incredible - it used to be Scottish managers who were regarded as the elite. Bill Shankly, Jock Stein, Alex Ferguson, Kenny Dalglish, and George Graham. Now it's the wise men from the top tip of Spain who are tip top.
While Athletic raid local clubs or lure players back with a promise of premium wages, La Real catch the kids young and have the most prolific academy in Europe