As a Yosemite gateway town, Mariposa's visitor patterns follow the park's. Summer (June to August) is the busiest time, with traffic on Highway 140 heavy on weekends and accommodation booking up weeks in advance. The valley is spectacular but crowded in summer; Mariposa provides better value than staying in the park.
Spring (April and May) is arguably the best time: wildflowers colour the foothills, waterfalls in Yosemite are at their fullest, temperatures are comfortable, and the crowds are lighter than in summer. The Highway 140 corridor through the Merced River Canyon is particularly beautiful in spring.
Autumn (September and October) offers a quieter version of summer with cooler temperatures. Winter can bring snow, and highway closures are possible on routes into Yosemite, but Mariposa itself rarely gets significant accumulation. Check CalTrans road conditions before any winter drive.