In the winter of 1919-20, the Spanish Flu epidemic that had begun in January 1918 was still rampaging around the globe; by the end of 1920 it would kill as many as 50 million people worldwide. Although Pleasanton was still a farming town with a population of fewer than 500 residing within the town limits (1100 if one counts unincorporated parts of the township), it was still vulnerable to the outbreak--in part because of the town's position on a railway line.
The end of January brought a fresh outbreak, and Pleasanton's government and citizens responded with the best tools at their disposal. A safe and effective flu vaccine would not be developed until the 1940s, so the primary response was to minimize contact, keeping people out of enclosed public spaces such as schools and theaters.
Pleasanton Times, 31 Jan. 1920