2003 Avalanch oil pressure light came on and it is low of oil but there is not oil on the ground........?

It burnt it. Depending on mileage, it's normal for high mileage engines to burn oil

You can also leak oil under pressure and not drip much if any when the car is at idle or turned off. Irodri911 is probably correct though, a small amount of oil will get past the cylinder rings and/or the valve seals and into the combustion chamber and burned when the engine is older and parts wear a bit. Quite a few vehicles even brand new will consume a small amount of oil between oil changes. The factory spec varies based on the vehicle but 1 quart every 3k to 5k miles is not uncommon. Just check your oil regularly and add a bit.