What is the fine-grained topic of the following text: The continuing success of Northern California’s existing co-ops, such as Rainbow Grocery, Other Avenues and the venerable North Coast Co-op in Arcata and Eureka in Humboldt County, has proven that collectively run markets with professionalism and financial savvy — those that made the passage from innocence to experience — are viable. Only return the topic.
The viability and success of co-operative markets in Northern California.