In 1969, one of the biggest bands ever to come out of the state of Texas was formed in Houston. And in the ensuing 50 years, ZZ Top has done its part to keep blues rock alive and well – and served as unofficial ambassadors of Texas to the rest of the world.  Sean Dunn, director of the new documentary “ZZ Top: That Little Ol’ Band from Texas,” talks about the band’s Texas roots, taking over MTV and those famous beards. The film screens Saturday at the Alamo Drafthouse Cedars as part of the Cacophony Film Festival.

Here are some highlights from the conversation:

On choosing to film the band playing in Gruene Hall in New Braunfels …

…. “We kinda wanted to put them in a room that felt a bit more intimate and give it more of a jam feel, where they were playing for each other rather than to a big hall full of fans.”

On how being from Texas is part of the band’s identity …

… “Over time, they kind of used the phrase ‘that little ol’ band from Texas’ – which was meant as kind of a diss and a derogatory term that a journalist came up with dismissing the band. And they turned that around and tried to turn it into a positive and took ownership of the fact that this is where they were from. Short answer is: I don’t think you can really tell the story of ZZ Top without talking about Texas and Texan identity.”

On maintaining a level of mystique over the course of 50 years …

… “That kind of attitude of building this identity that has remained fixed in time has served them over the long term. At the time – in the early ’80s – when they grew these beards, it was an anomaly. But in a weird way, they could keep getting older, but you wouldn’t be able to tell how old these guys were. They kind of became these masks in a way, which kind of gave them a timeless quality.”