The town Steinbeck is referring to is La Paz, Mexico. It is the capital of Baja, California Sur and is located at the southern tip of the Baja Pennisula. It is part of Mexico. Although it is a great tourist attraction now, it was a quiet little fishing town when Steinbeck writes his parable.
His reference to the town that "keeps track of itself and all if its units" means that as long as people were doing what they were suppose to do, it didn't cause any ripples. That person could leave and disappear and no one would notice. The poor remained poor, and the rich remained rich, and nothing changed. But the minute that someone tried to step outside of the prescribed lines of society, everyone knew. When the poor Indians had tried to find someone who would give them more money for their pearls in the city, they found someone who would take their pearls into the city to trade, but no one ever returned and they lost their pearls. The priest told these poor men and women that
"The loss of the pearl was a punishment visited on those who tried to leave their station." (pg 46)
Kino was a member of the poor Indian community, and now he had the pearl. It was a great pearl and would give him the money he needed to move out of his station. Everyone in town knew he was going to sell it that day. Word had spread.