Friends and acquaintances gathered Thursday to discuss the Aug. 20 invitation-only service, which will be six months after Thompson shot himself in his Woody Creek home.
Jon Equis, the event producer working with Thompson's family, said the tower would be 12 feet wide at the base and 8 feet wide at the top, where a cannon would be placed.
Depp, who portrayed the author in the movie version of Thompson's book "Fear and Loathing in Las Vegas" will pay for the tower, designed to resemble Thompson's "gonzo fist" emblem.
As Thompson requested, his ashes will be shot out of the cannon onto his property.
Equis said the tower would be constructed far from Woody Creek Road and covered with a black drape before the service to discourage tourists. A public event was to be planned later to commemorate the writer's life.
The August event will consist of "spoken word and live entertainment," Equis said. The cannon will be fired around sunset.
The event organizers must get the plans reviewed by the Pitkin County Community Development Department, but Thompson's widow, Anita Thompson, was supportive. She said the event would be a celebration.