Whisk together salt, pepper, cumin, chili powder, garlic powder, onion powder, paprika, oregano, crushed red pepper flakes and beef broth in a small bowl. Set aside.
Heat olive oil in a large skillet over medium high heat. Once oil is hot, sear the roast on all sides until golden brown (using large tongs to flip roast). *
Place the roast in a 6-quart slow cooker. Pour beef broth mixture over roast evenly. Top with salsa. Cover and cook on low heat for 8 hours or on high heat for 4 to 5 hours (or until tender).
Carefully remove roast from slow cooker and place on a platter, cutting board or rimmed baking sheet. Shred using 2 forks, discarding any fat.
Skim off any fat that has risen in the liquid in the slow cooker. Remove liquid from slow cooker to leave about 1 ½ cups (or leave all the liquid if you prefer it very juicy). Return shredded beef to liquid mixture and toss to coat with liquid as evenly as possible.