  We report a measurement of the single top quark production cross section in
2.2 ~fb-1 of p-pbar collision data collected by the Collider Detector at
Fermilab at sqrt{s}=1.96 TeV. Candidate events are classified as signal-like by
three parallel analyses which use likelihood, matrix element, and neural
network discriminants. These results are combined in order to improve the
sensitivity. We observe a signal consistent with the standard model prediction,
but inconsistent with the background-only model by 3.7 standard deviations with
a median expected sensitivity of 4.9 standard deviations. We measure a cross
section of 2.2 +0.7 -0.6(stat+sys) pb, extract the CKM matrix element value
|V_{tb}|=0.88 +0.13 -0.12 (stat+sys) +- 0.07(theory), and set the limit
|V_{tb}|>0.66 at the 95% C.L.
