Sounds like you may have "glazed" your pads and rotors. New brake pads require a break-in period before you subject them to hard long braking.
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Even when you already have your disks broken in, long drag braking can cause them to overheat and fade. This leads to a kind of vicious cycle in which the brake is less effective and you start using it even more.
Brakes are designed to cool themselves with the available airflow, even a few seconds every minute can make a difference. Of course, that's easier said than done when you feel like you are over your head. Braking effectively is a skill that takes practice. If you are dragging the brakes constantly to control your speed, you'll be better off coming to a complete stop and regrouping.
Sometimes, you just need to walk stuff when you are over your head.
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