Rio Grande Mexican Restaurant is hosting a thirtieth-birthday block party all day on Saturday, June 18, in Fort Collins, where it all began. We caught up with co-founder and owner Pat McGaughran for a Facebook Live chat this week, and guess what everyone wanted to know? The secret behind the Rio's infamous margs — limited to three per customer. Asks Rioette: 

What do you put in those margaritas?

Responds Jon: 

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The hush hush is actually apple juice.

Adds Sheila: 

I was told the secret is Mountain Dew!!

Even after thirty years, McGaughran isn't ready to spill all his secrets. You can learn more by reading Mark Antonation's interview with McGaughran, watching the Facebook Live chat, or just heading to Fort Collins tomorrow to do some research on those margs yourself.