When enacting , a zoning ordinance in 1972, the Los Angeles City Council was not required to render a written Negative Declaration to evidence its determination that the ordinance would have no significant effect on the environment. There was no express requirement of such writing and no basis for implying one. The city council proceeded in a manner required by law, and the evidence before us fully supports the determination that the proposed test holes will have no significant effect on the environment.
In enacting the present zoning ordinances, the city council performed a legislative function. (Johnston v. City of Claremont (1958) 49 Cal.2d 826, 835-836 [323 P.2d 71]; Clemons v. City of Los Angeles (1950) 36 Cal.2d 95, 98 [222 P.2d 439]; Lockard v. City of Los Angeles (1949) 33 Cal.2d 453, 460 [202 P.2d 38].) As recognized by the majority {ante, pp. 74-75), the city council was not required to hold an evidentiary hearing, and judicial review of the council’s action is governed by traditional mandamus principles rather than the administrative mandamus procedure of Code of Civil Procedure section 1094.5. (Pub. Resources Code, §§ 21168, 21168.5, 21168.7.) Thus the requirement of administrative findings set forth in section 1094.5 (see Topanga Assn, for a Scenic Community v. County of Los Angeles (1974) 11 Cal.3d 506, 511, 522 [113 Cal.Rptr. 836, 522 P.2d 12]) is not applicable to the adoption of the ordinances,1 and no other principle of general law or charter provision has been cited or found requiring the Los Angeles City Council to make findings of fact in adopting ordinances.
*90There is no express provision in the California Environmental Quality Act (Pub. Resources Code, § 21000 et seq.) (hereinafter CEQA),2 as enacted in 1970 or in its present form, requiring prior to project approval either “findings” or any written determination that a project will not have a significant effect on the environment. To the contrary, the language of CEQA indicates that written findings were not contemplated for such a determination. Section 21168.5 provides that abuse of discretion may be established either by showing that the agency failed to proceed in a manner required by law or by showing that the “determination or decision” is not supported by substantial evidence. (§ 21168.5; italics added.) Clearly the act contemplates only that the determination be made. If the Legislature had intended written findings, it could easily have said that abuse of discretion is established when the decision is not supported by the findings, or the findings are not supported by substantial evidence. (Cf. Code Civ. Proc., § 1094.5; Topanga Assn, for a Scenic Community v. County of Los Angeles, supra, 11 Cal.3d 506.)3
*91Further support for the conclusion that CEQA did not require a written Negative Declaration is furnished by this court’s decision in Friends of Mammoth v. Board of Supervisors (1972) 8 Cal.3d 247, 270 [104 Cal.Rptr. 761, 502 P.2d 1049]. Friends of Mammoth expressly rejected a requirement of written findings when an agency approves a project after preparation of an environmental impact report. It appears inconsistent to imply a requirement of written findings for a determination that no environmental impact report is necessary when this court refused to imply a requirement for such findings for the more important decision whether to approve a project in light of the admitted adverse environmental effects disclosed by an environmental impact report.
Sound practical considerations militate against the implication of formalistic requirements into the legislative process. When the legislative body has complied with all substantive requirements and all express formalistic requirements, the majority’s will should not be frustrated by adding a formalistic requirement, the necessity for which could only be foreseen by those possessing acute clairvoyance.
The unreasonableness of implying a formalistic requirement into the legislative process is dramatically illustrated by the requirement implied by the majority today. Unless the legislative body somehow anticipated today’s implied requirement of a written determination, every ordinance affecting the use of land adopted between the enactment of CEQA in 1970 and the adoption of the guidelines in 1973 has been improperly adopted, including ordinances involving projects where “it can be seen with certainty that the activity in question will not have a significant effect on the environment.” Although projects coming within the quoted term are presently exempt from the written Negative Declaration requirement expressly imposed by the guidelines (Cal. Admin. Code, tit. 14, § 15060), the guidelines with the three-tiered structure relied upon by the majority were not adopted until 1973.4 Probably thousands of ordi*92nances including those coming within the quoted term were not properly adopted under today’s majority opinion.5
In imposing the requirement of a written determination on the legislative process, the majority also starts us down a dangerous path which, if followed in the future, will have unfortunate consequences. The majority implies the requirement not on the basis of language dealing with writings; the only language relied on is that set forth in the purposes of the act. However laudable or noble the purposes of a statute, the method to be followed by the city council in adopting ordinances under it should remain the same unless the statute itself or authorized regulations provide for a different method of enactment. To vary the method of enactment, depending upon judges’ opinions as to the virtues of statutory purpose, is an improper interference with the legislative process and can only lead to confusion and frustration of the majority’s will.
Since the city council was not required to produce written findings of fact or a written determination in the form of a Negative Declaration, it must be presumed that official duty has been regularly performed (Evid. Code, § 664) and that the legislative body has ascertained the existence of those facts essential to its action (e.g., Orinda Homeowners Committee v. Board of Supervisors (1970) 11 Cal.App.3d 768, 775 [90 Cal.Rptr. 88]). As the council passed the ordinances without preparing an EIR, it must be presumed it had determined the informational holes would not have a significant effect on the environment.
Evidence of events occurring after the 17 October 1972 passage of the ordinances, including submission of declarations by the councilmen and the council resolution of 8 January 1973 (both of which stated that the ordinances were approved on 17 October 1972, because the council believed the limited drilling would have no significant effect on the en*93vironment) does not establish that the council failed to make the determination. If anything the evidence tends to support the presumption that the determination was made.6 In any event it was unnecessary for defendants to prove that the determination was actually made, for the issue should have been resolved in their favor when plaintiffs failed to adduce evidence sufficient to overcome the presumption.
I conclude the council proceeded in a manner required by law. The inquiry thus is whether the council’s determination is supported by substantial evidence. (§21168.5.) There is ample evidence in the record to sustain the decision. The ordinances contemplated drilling of extremely limited scope. Only two informational test bore holes were authorized; the entire operation was to last only 90 days, with the rigs to be removed upon completion; and a number of other restrictions and conditions were imposed on the project. Under no circumstances was commercial production of oil to be permitted. With respect to the impact of the drilling vibrations, Occidental produced expert testimony that vibrations from the drilling at a point 150 feet from the drill site would be less than those caused by movement along the nearby highway, and 5 to 10 times less than the ambient vibrations outside the courtroom door. As to the possibility of a “blowout,” there was evidence that the incidence of blowouts at urban drill sites was only 2/10ths of 1 percent.7 Occidental also introduced photographs demonstrating methods by which the drill site would be made aesthetically consonant with adjacent land uses. The foregoing represents only a sampling of the evidence marshalled by Occidental to dispel any doubts about the environmental effect of the test holes.
The limited drilling authorized by the ordinances is a “basic data collection” or “resource evaluation” activity inasmuch as the object of the drilling is to determine the size and yield of the Riviera oil field and obtain data essential to a thorough environmental assessment of oil production. Unless the city council determines that this activity will result in a “serious or major disturbance to an environmental resource” the proposed test holes will be categorically exempt from CEQA under the present guidelines. (Cal. Admin. Code, tit. 14, § 15106.) In the event *94the council concludes the drilling will not result in a serious or major disturbance to an environmental resource, the city council will not be required to render a written Negative Declaration nor any'writing whatsoever prior to approval of the ordinances, for the guidelines do not require any writing for a determination that a project is categorically exempt from CEQA. The agency “may” file a brief notice of exemption but is not compelled to. (Cal. Admin. Code, tit. 14, § 15035.5.) This observation only highlights the futility, as well as the inappropriateness, of the requirement which the majority implies today.
I would affirm the judgment.8
McComb, J., and Burke, J.,* concurred.
The petition of respondent Occidental Petroleum Corp. for a rehearing was denied January 29, 1975, and the opinion was modified to read as printed above. Molinari, J.,† sat in place of Mosk, J., who deemed himself disqualified. Clark, J., was of the opinion that the petition should be granted.
The statement of the majority that Occidental in seeking rezoning was circumventing the requirement of a conditional use permit is misleading and unfortunate. (Ante, p. 76.) In Topanga, the court stated that rezoning was the appropriate method to obtain a special use for a large parcel. (11 Cal.3d at p. 522.)
Unless otherwise stated, all statutory references are to the Public Resources Code.
The absence of an express statutory requirement of “findings” distinguishes the instant case from Topanga. In Topanga we determined that the administrative man-dam.us procedure of Code of Civil Procedure section 1094.5, by providing that abuse of discretion is established if the administrative decision “ ‘is not supported by the findings, or the findings are not supported by the evidence,’ ” required that agencies subject to review by administrative mandamus must set forth specific findings. (11 Cal.3d at p. 515.)
Our reasoning in Topanga was that the Legislature must have intended specific findings in view of the fact that it established the reviewing court’s duty to compare the evidence and ultimate decision to “ ‘the findings’ . . .” (11 Cal.3d at p. 515; italics added.) We noted that “[i]f the Legislature had desired otherwise, it could have declared as a possible basis for issuing mandamus the absence of substantial evidence to support the administrative agency’s action.” (11 Cal.3d at p. 515; italics added.) On the basis of the Topanga rationale we must conclude the Legislature did not intend findings in the case of CEQA, for it has provided that the evidence be compared only to the “determination or decision” of the agency. (§ 21168.5.)
The majority disclaims having imposed any requirement of findings on the legislative process, stating that it requires only that the determination of no significant effect on the environment be put in writing. (Ante, p. 81.) The majority reasons that in the absence of such writing there is no way a court can tell if the agency actually made the determination. If this is the case, the requirement would seem fully satisfied by either the declarations of the councilmen submitted prior to trial or the council resolution of 8 January 1973. These eliminate the majority’s objection to the record, .i.e., they show that a determination was in fact made prior to approval of the ordinances.
By the lengthy impeachment of the council resolution (ante, pp. 82-88), however, the majority requires more of a negative declaration than a mere written statement of the fact of determination. The resolution adequately satisfied the only formal requirement purportedly imposed by the majority. By going behind the resolution, the majority in effect requires not only that the determination be reduced to writing but also that it affirmatively evidence proper supporting reasons.
The 1972 amendments to CEQA provide that the guidelines shall contain a list of classes of projects which the Secretary of the Resources Agency has found do not have a significant effect on the environment. (§ 21084.) A project falling within these classes is exempt from the provisions of CEQA. (§§ 21084, 21085.) The guidelines presently contain a list of such projects. (Cal. Admin. Code, tit. 14, §§15100-15112.) However, CEQA itself does not exempt any projects other than ministerial ones and emergency repairs to public service facilities (§§ 21080, 21085); hence there were no projects other than those mentioned in CEQA which were exempt until promulgation of the guidelines.
In general the guidelines establish a three-tiered structure—projects for which an EIR is filed; projects for which a Negative Declaration is filed, and categorically exempt projects. However, only a two-tiered structure is provided as to the type of *92ordinance before us. Activities for the purpose of “basic data collection” or “resource evaluation” are categorically exempt unless the activity will result in a “serious or major disturbance to an environmental resource.” (Cal. Admin. Code, tit. 14, § 15106.) If the activity would result in a “serious or major disturbance to an environmental resource,” it would seem perforce that an EIR is required. If not, the activity is exempt. In the instant case, if the city council finds such a disturbance, an EIR m.ust be prepared. If it does not so find, there is not even a requirement of a Negative Declaration, for the guidelines do not require filing of a Negative Declaration when a public agency approves a project that is categorically exempt. (Cf. Cal. Admin. Code, tit. 14, § 15035.5.)
Since the majority has implied the writing requirement, it could imply the exemption too—once the fabric is woven from thin air, it may be embellished at will. Nevertheless, implication of the requirement and the exemption in the absence of any language dealing with writing requirements or exemptions from them appears a clear invasion of the legislative process.
In a 17-page letter of 3 October 1972 the city attorney advised the city council that all projects which may have a significant effect on the environment required preparation of an EIR and specifically concluded that all zone changes should be accompanied by an EIR if the permitted use may have a significant effect on the environment.
The experts for plaintiffs conceded that the incidence of blowouts was “very low” and that the petroleum industry had developed “very sophisticated means” of preventing such accidents.
The majority balks at resolving a number of questions highly pertinent to cases arising^ under CEQA, which I feel leaves the disposition of this case and others uncertain to an unfair extent. Specifically, the majority does not decide what is required in a Negative Declaration and declines to formulate a more definite test for determining what constitutes a “significant effect” on the environment. Thus, while the city council must now redetermine the environmental issues involved, it does not even have assurance that adherence to the standards set forth in the guidelines is the proper course to pursue. The majority remands the case without informing the council what is expected of it in future deliberations.
The unwarranted aspersions cast by the majority on the application of the political process in this case perhaps explain the majority’s willingness to reach its desired result without confronting the important questions of law. The record, however, provides no basis for believing the political channels were abused in any manner.
Retired Associate Justice of the Supreme Court sitting under assignment by the Chairman of the Judicial Council.
Assigned by the Chairman of the Judicial Council.