From their FB page:
For the past 18 years, El Dia de San Juan Fiesta has been a cultural, historic and educational celebration to welcome the monsoons to our Tucson desert. The stories of the celebration of El Dia de San Juan date back to as early as 1915 when Tucsonans would gather around the Santa Cruz River to wish, hope and pray that the monsoon would come in abundance but without destruction or harm.
Every year this traditional celebration is hosted in Ward 1 on June 24th, the day of el Dia de San Juan el Bautista. This free, family event includes wonderful cultural music and traditions of Mariachi and Ballet Folklórico Xóchitl de Tucson performances. There are piñatas for the kids, with local vendors and food booths, informational booths, and games all until the closing of the event.
When: Wednesday, June 24, 2015
Where: South East corner in the big lot by the Streetcar at the Mercado San Agustin, 100 South Avenida del Convento (west of the I-10).
Time: The event begins with a procession at 5:00 PM at the Cushing Street Bridge.