Home 10th Annual Marble Falls Soapbox Classic Adult Soapbox Derby Historic Downtown Marble Falls, Texas Arbor Day Weekend April 26-28, 2019 RACING REGISTRATION OPENS FEBRUARY 1st. The DEADLINE is April 5th. Racing slots are limited and first come-first serve. Do not show up on race day and expect to race if you are not registered. Click HERE for more information. Yes…. we have moved the races from the heat in June to the cooler temperatures in April! SPECIAL THANKS TO OUR EVENT SPONSORS! We simply could not do it without your help.