IS this W-2 for the same employer?
1) IF it is, it is likely you were supposed to enter the CO information as a second state line on the one single W-2 entry area...especially if the sum of the CA and CO box 16 values equals the box 1 value on the one that does have $$$ in box 1.
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2) If it is from a different employer...look again at the W-2, many times there are multiple copies of the W-2 in case you have to mail them in...and maybe a different one has all the boxes 1-14 values.
Otherwise, you need to get hold of that CO employer to get a corrected W-2