Hybridization - how does carbon form tetrahedral structures?

As the energy difference between the 2s A.O. and the 2p A.O.s isn't very large the, an electron from the 2s A.O. can be promoted to the 2px A.O. This process is known as excitation:

C (ground state): 1s², 2s², 2p_x¹, 2p_y¹, 2p_z⁰

C* (excited state): 1s², 2s¹, 2p_x¹, 2p_y¹, 2p_z¹

This provides carbon with four unpaired electrons that are able to form bonds, however at this stage these are not equivalent. We know that the methane structure has four equivalent bonds.

How does carbon attain four equivalent orbitals?