The Supreme Court vacated our original divided disposition in this case, reported at 861 F.2d 1421 (9th Cir.1988) and remanded for further consideration in light of Neitzke v. Williams, 490 U.S. 319 , 109 S.Ct. 1827 , 104 L.Ed.2d 338 (1989). We have given further consideration after requesting briefs from the parties as to the bearing of that decision on this case.

The appellant, Mike Hernandez, is a prisoner proceeding in forma pauperis in suits against prison officials. At issue are the district court’s dismissals of complaints alleging 42 U.S.C. § 1983 violations. The district court dismissed all the claims as “frivolous” under 28 U.S.C. § 1915 (d) and Hernandez appealed.

In our original opinions, we unanimously affirmed the district court’s dismissal of plaintiff’s procedural due process claims and his claim that prison officials violated his eighth amendment rights by depriving him of a mattress for one night. We held that no amendment could cure the defects in those allegations. See Franklin v. Murphy, 745 F.2d 1221 , 1228 n. 9 (9th Cir.1984). Those rulings are not affected by the subsequent grant of the defendants’ petition for certiorari.

In the original opinions, a majority also reversed the district court’s dismissal of Hernandez’ claims of rape, other physical abuse, and deprivation of footwear. The majority held that it was improper for a district court to dismiss a pro se complaint as frivolous under section 1915 unless claims were “patently meritless.” We also held that the standard of “frivolousness” of section 1915(d) is not the same as the Federal Rule of Civil Procedure 12(b)(6) legal standard for dismissal for failure to state a claim. Hernandez, 861 F.2d at 1425 . Relying upon this court’s decision in Franklin , we held that a pro se prisoner complaint may not be dismissed under section 1915 unless it has no “ ‘arguable substance in law [or] fact.’ ” Hernandez, 861 F.2d at 1425 , quoting Franklin, 745 F.2d at 1227 .

The Supreme Court has now held in Neitzke , as a majority of us originally concluded in this case, that the standard of “frivolousness” is not the same as the Rule *575 12(b)(6) standard, and that a complaint should not be dismissed under section 1915 simply because it fails to state a claim. The Supreme Court cited with approval our decision in Franklin v. Murphy in holding that a complaint is frivolous when “it lacks an arguable basis either in law or in fact” and that section 1915 “embraces not only the inarguable legal conclusion, but also the fanciful factual allegation.” Neitzke, 109 S.Ct. at 1831 .

In this case, the most troublesome allegations are appellant’s claims that he was drugged and homosexually raped over twenty times by inmates and prison officials at different prisons. Because the claims lacked factual recitations of time and place and persons responsible, the complaints failed to state rape claims upon which relief could be granted under the Rule 12(b)(6) standard. Nevertheless, because rape by prison guards or deliberate indifference by prison guards to rape by inmates would raise constitutional concerns, the claims were not patently without legal substance. Although the claims of such repeated similar events undoubtedly involved some exaggeration, a majority of us were unable to say with certainty that none of them occurred and that the claims were therefore lacking in any factual basis so as to be deemed “fanciful” under section 1915(d).

The appellees now ask us to reconsider that ruling in light of the Supreme Court’s remand. The Supreme Court in Neitzke said that under section 1915 judges may dismiss as frivolous not only claims based on patently meritless legal arguments, but those premised on baseless factual allegations as well. This holding is fully consistent with the prior law of this circuit. See Franklin, 745 F.2d at 1227 . The defendants now focus on the Supreme Court’s statement in Neitzke that examples of baseless factual claims are “fantastic or delusional scenarios.” 109 S.Ct. at 1833 . The defendants ask us to hold that Hernandez’ allegations of 28 rapes are “fantastic or delusional scenarios,” and affirm the district court’s dismissal. If we were to affirm the district court’s dismissal of all the claims as factually frivolous, however, we would have to hold that all 28 rapes were delusions and that none of them occurred. While it is hard to believe that so many similar incidents actually happened, we cannot say that none of them occurred without making the kinds of credibility determinations that are impermissible in deciding whether a claim is baseless under section 1915. See Franklin, 745 F.2d at 1228 .

Under Neitzke , we do not believe that a claim can qualify as patently “delusional” or “hallucinatory” unless it rests upon facts which the court knows could not have occurred. The provision for judicial notice in Federal Rule of Evidence 201 provides guidance. It states: “A judicially noticed fact must be one not subject to reasonable dispute in that it is either (1) generally known within the territorial jurisdiction of the trial court or (2) capable of accurate and ready determination by resort to sources whose accuracy cannot reasonably be questioned.” Fed.R.Evid. 201(b). We accept this as one useful standard in determining whether a claim is patently frivolous as “founded on wholly fanciful factual allegations.” Hernandez, 861 F.2d at 1426 (quotation omitted). We cannot conclude that the plaintiff’s claims of rape are contrary to any facts that are “generally known,” nor can we ascertain the truth of the allegations by looking to any readily available, accurate source. We therefore conclude that the district court in this case erred in dismissing the rape claims at this stage of the litigation as fanciful.

The appellant should be permitted to amend the claims to provide more specific factual recitations of the time and place of each of the rapes and conduct on the part of prison officials which violated constitutional standards. Only when it is clear that a claim lacks legal or factual basis may it be dismissed as frivolous. Neitzke, 109 S.Ct. at 1831 . Accordingly, while we affirm the district court’s dismissal of appellant’s procedural due process claim and his eighth amendment claim based upon deprivation of a mattress, we reverse the district court’s dismissal of the remainder of *576 the claims. It is not yet apparent that those claims lack either legal or factual basis.

AFFIRMED in part; REVERSED and REMANDED in part.