Pickens launched the letter-writing campaign in a new tack in her long-running campaign to stop the roundups and provide a better long-term home for the more than 30,000 horses held by federal authorities in captivity.
She says that by hand-delivering mail, supporters will circumvent reported problems with online submission forms, and avert any possibility that their emails get deleted or phones are left unplugged.
Pickens says she will personally hand-deliver each and every letter that supporters write by horse, in a nod to the historic Pony Express mail service.
"This is a very important issue to hundreds of thousands of people that have pleaded with our government to stop gathering our wild horses," she said.
"This way, they cannot unplug their phones, make their website impossible to send a comment to, or delete emails. These are GOING to get to Washington. I promise you that!"
Pickens proposes a huge sanctuary, possibly in Northern Nevada, in which the horses currently held in captivity could be allowed to roam free. She said her plan would be more cost-effective for taxpayers and has strong tourist potential.