Is a sentence which falls within statutory limits subject to appellate review?

A sentence which falls within statutory limits is generally not subject to appellate review absent an abuse or abdication of discretion by the district court. United States v. Rachels, 820 F.2d 325, 328 (9th Cir.1987); United States v. Chiago, 699 F.2d 1012, 1014 (9th Cir.1983), cert. denied 464 U.S. 854 (1983). "Whether sound discretion has been exercised must be answered in each case through a thorough review of the record." United States v. Barker, 771 F.2d 1362, 1366 (9th Cir.1985). The relevant inquiry is whether the "four corners of the record" reflect that the district court properly considered those factors necessary to insure an individualized sentence. Id. at 1365-66. An abuse of discretion will be found where the district court imposes sentences purely on a mechanical basis. Id. at 1364; see also United States v. Potts, 813 F.2d 231, 233 (9th Cir.1987).