If you drive from Denver to LA during February, you must cross the Rocky Mountains or detour south of them during the middle of winter. Heavy snow storms can close some of the roads, so you should pay attention to your route and to the weather conditions. Fortunately, most of the main highways are usually cleared within a few hours or a few days at the most, so you can always get through. If you pay attention to the weather forcasts, and avoid drifvng into any big snow storms, you should be fine.
The safest winter route might be south on route 24 to New Mexico, then west on route 40, parallel to old route 66, across to Albuquerque, Flagstaff, the Grand Canyon, Las Vegas and finally LA. This takes you well south of Bryce Canyon and Zion, but they are in the mountains at higher altitudes where there is likely to be snow. Even the Grand Canyon South Rim Visitor Center is at 7,000 feet, and could have snow.