This is an original proceeding instituted on August 26, 1977, by petitioners, the Ada County Assessor, the Ada County Clerk of the District Court and Ex-Officio Auditor, the Ada County Property Owners Association, and four taxpayers. Petitioners seek a peremptory writ of prohibition against respondents, the Ada County Board of Commissioners, the Ada County Board of Equalization, the Idaho State Tax Commission, and their members. Petitioners seek to prevent the Ada County Board of Equalization from further acting on the existing 1977 Ada County Real Property Assessment Roll, and the Board of County Commissioners from interfering with the Assessor’s supervision of his office personnel and from transferring funds budgeted to the Assessor’s office. Additionally petitioners seek to prohibit the Idaho State Tax Commission from acting on or certifying to the Ada County Clerk of the District Court and Ex-Officio Auditor the existing 1977 Ada County Real Property Assessment Roll and from issuing orders or directives to the Ada County Assessor that interfere with the direct management of his office.
Subsequent to the date this petition was filed, the named respondents filed their motion to dismiss the proceedings and the cause was set for argument on September 21, 1977. In the meantime, various Ada County Taxing districts and municipalities moved to intervene and to dismiss the petition. At argument the parties agreed that the intervenors should be treated as additional respondents.
In an order issued on May 7,1976, by the State Tax Commission, the Ada County Assessor and the Ada County Board of Equalization were directed to conduct a revaluation of all property in Ada County by June 1, 1977, with these values to be shown on the 1977 assessment rolls and used for 1977 tax assessments. The order also provided:
“The county shall retain the services of a qualified professional independent appraiser for the purpose of conducting the valuation program either as an independent contractor or in conjunction with the Ada County assessor’s office.”
*751On June 14, 1976, Max P. Arnold and Associates, Inc. entered into a written “CONTRACT FOR APPRAISAL SERVICES” with Ada County, the agreement being approved and executed by the Assessor, J. L. “Mike” Clark, and each of the then members of the Board of County Commissioners.
On May 24, 1977, while the reappraisal program was nearing completion, the State Tax Commission issued a supplemental order. Reciting in its findings that there appeared to be a need to reform procedures in the offices of the Ada County Assessor, Auditor and Treasurer to insure that all tax data would be properly and uniformly processed for the valuation of the property, assessment, equalization, levy and collection of taxes for 1977 and future years, the Commission then directed Ada County, its Board of Commissioners and Board of Equalization to
1. Review, by the Board of Equalization, all values established by the re-appraisal program, including, but not limited to those protested by taxpayers;
2. Extend by 90 days the time to determine all protests, and to submit to the State Tax Commission an estimated abstract of the rolls on or before July 25, 1977.
3. Establish and maintain a parcel numbering system with the data processing equipment and procedures to be used in the county offices; to map, and inventory all new property and to verify all taxing district boundaries.
4. Establish, under the Board of County Commissioners, an independent and permanent data processing audit system to review and audit all procedures and results of valuation, assessment, equalization, levy, collection and payment of taxes.
5. Supervise, through the Board of County Commissioners, the activities of the county and county officers relating to the assessment, levy and collection of the taxes at all stages.
6. Submit within 45 to 60 days a written report showing the steps taken to implement the provisions of the order and progress made.
After the issuance of this Supplemental Order, the present Board of County Commissioners issued a “policy statement” on June 30, 1977. This statement provided that Max P. Arnold and Associates, Inc., would be retained to review and process appeals of the 1977 Notice of Valuations and to review the 1977 roll as agents of the Board of Equalization for the purpose of any recommendation on final actions on the roll, and that the reappraisal function for purposes of the 1978 roll would be returned to the office of the Assessor. The policy statement also included a staffing plan for a reappraisal office and a staffing plan and tentative program for a “permanent audit division,” which was to audit independently the “procedures and results” of the taxing system. The policy statement also provided for transferring funds from the Assessor’s office in order to accomplish the continuing reappraisal, but made no provisions for requiring the consent or supervision of the Assessor.
By the end of June, 1977, the reappraisal project was completed and the tax roll for 1977 prepared by Arnold & Associates. The Assessor “transmitted” the roll to the Board of County Commissioners on June 24, 1977, stating he was unable to verify the rolls (required by I.C. §§ 63-318 and 63-319) because he had no knowledge of its accuracy. The Board of Equalization accepted the roll without verification and delivered it to the Auditor for preparation of abstracts. On July 25, 1977, the Auditor submitted the abstract of the assessment roll to the State Tax Commission. This abstract was certified by the Auditor and examined and approved by the Assessor on the date of its transmittal. The State Tax Commission approved the abstract as modified on August 22,1977 (the fourth Monday of August), and it was certified on August 26, 1977, the day this proceeding was instituted.
Petitioners specifically seek to prohibit the Board of County Commissioners of Ada County from the following acts:
*752“a. From acting further as an Ada County Board of Equalization on the existing 1977 Ada County Real Property Assessment Roll.
b. From interfering in any unlawful manner with the Ada County Assessor’s supervision of personnel employed by his office.
c. From transferring funds lawfully budgeted or dedicated to the use of the Ada County Assessor’s office.”
They also seek to prohibit the Idaho State Tax Commission from the following acts:
“a. From acting on or certifying to the Ada County Clerk of the District Court and the Ex-Officio Auditor the existing 1977 Ada County Real Property Assessment Roll.
b. From issuing orders or directives to the Ada County Assessor which intereferes [sic] with the direct management of his office.”
Article 5, Section 9 of the Idaho Constitution grants this court original jurisdiction to .issue writs of prohibition. The function of a writ of prohibition and the circumstances in which it is appropriate are generally set out in Title 7, Chapter 4 of the Idaho Code. As therein defined, a writ of prohibition is an extraordinary writ issued to arrest the proceedings of a tribunal, corporation, board or person acting without or in excess of its jurisdiction. I.C. § 7-401. By this writ a court intervenes in judicial or quasi-judicial proceedings to prevent acts or proceedings without or in excess of authority. The remedy is therefore preventive in nature. In re Miller, 4 Idaho 711, 43 P. 870 (1896). However, even in cases where jurisdiction may be lacking or exceeded, a writ of prohibition will issue only if no plain, speedy and adequate remedy at law is available. I.C. § 7-402. See Pfirman v. Probate Court, 57 Idaho 304, 64 P.2d 849 (1937); Murphy v. McCarty, 69 Idaho 193, 204 P.2d 1014 (1949).
In defining the writ of prohibition, the Idaho Code merely codifies the characteristics of the common law writ. Stein v. Morrison, 9 Idaho 426, 75 P. 246 (1904). Under Idaho common law, the writ of prohibition is a discretionary remedy, granted only when the court is satisfied that the remedy is appropriate. Rust v. Stewart, 7 Idaho 558, 64 P. 222 (1901). As we held in that case, this extraordinary writ will not be granted when its appropriateness or effectiveness is doubtful. Thus an applicant bears the burden of showing that a respondent is acting without or in excess of its jurisdiction and that the writ will effectively prevent the respondent from so acting. The court will not, however, issue a writ as an idle gesture, i. e., where no act in excess of jurisdiction can be prevented.
It follows that a past act will not be subject to a writ. As this court stated in Bellevue Water Co. v. Stockslager, 4 Idaho 636, 43 P. 568 (1895):
“The writ of prohibition will not issue where the act to be restrained has already been performed, even where the act has been performed during the pend-ency of the application for the writ, for the reason that the writ would be without any effect whatever.” 4 Idaho at 641, 43 P. at 569.
See also: La Salle Extension Univ. v. District Court, 52 Idaho 559, 16 P.2d 1064 (1932), and Nelson v. Marshall, 94 Idaho 726, 497 P.2d 47 (1972), citing Bellevue Water, supra, with approval.
A. Restraints sought against the Idaho State Tax Commission
We turn to petitioners’ request that this court prohibit the Idaho State Tax Commission from “acting on or certifying to the Ada County Clerk of the District Court and Ex-Officio Auditor the existing 1977 Ada County Real Property Assessment Roll.” It is documented that on the day this action was filed, i. e. August 26, 1977, the State Tax Commission acting as the State Board of Equalization had already reviewed and approved the abstract of the real and personal property roll of Ada County. The abstract of the property roll was formally certified on August 26, 1977. It is further undisputed that at the time of certification no member of the Commission had knowledge of the filing of the instant *753action and that since the assessment roll had already been certified and returned to the County, there were no further acts required by the Commission. In other words, by the time the instant action had been filed, all actions in the certification procedure had been completed by the State Tax Commission and nothing remained to be accomplished concerning the 1977 tax roll for which the writ of prohibition could have issued. Under such facts the writ cannot issue.
Next, petitioners request that the State Tax Commission be prohibited from issuing orders or directives to the Assessor that interfere with the direct management of his office. Again, the actions petitioners would have this court enjoin have been completed. Furthermore, petitioners fail to point out where there is any threat of such action being taken in the future. We therefore conclude that the writ of prohibition should not issue to the Commission.
B. Restraints sought against the Ada County Board of Commissioners and Ada County Board of Equalization
Petitioners seek to prohibit further action by the County Board of Equalization on the 1977 tax roll, which is now complete. The crux of petitioners’ argument is that because the independent appraisal carried out by the County Commissioners and Max Arnold was not within the County Commissioners’ jurisdiction, all subsequent acts by the County Board of Equalization are in excess of its jurisdiction and, therefore, should be prohibited. This argument is untenable.
The court first notes that the reappraisal was completed at least two months before this action was filed. Because a past act cannot be prohibited, Bellevue Water Co. v. Stockslager, supra, it need not be decided, and we expressly decline to decide, whether the Commissioners exceeded their jurisdiction in their dealings with Arnold & Associates.
Any subsequent acts concerning the roll that petitioners ask the court to prohibit are required by statute and therefore fall within the jurisdiction of the County Board of Equalization. Idaho Code §§ 63-401 et seq. not only empower, but require, county commissioners to meet as a board of equalization to hear and determine protests and claims for tax exemptions. Title 63, Chapters 9 and 10 of the Idaho Code require the determination of mill levies, computation of the tax due on each parcel and mailing of tax notices to taxpayers. Thus the only remaining actions to be taken on the 1977 roll that might have been prohibited when this suit was filed were authorized by statute. As petitioners themselves have pointed out, a writ of prohibition is issued to intervene in and to prevent further actions in excess of jurisdiction. The writ is not a vehicle for forcing review of past extra-jurisdictional actions by prohibiting present actions plainly within a respondent’s jurisdiction. The court therefore declines to prohibit respondents from further using the 1977 Ada County tax roll.
Petitioners next seek to prohibit the County Boards from interfering in any unlawful manner with the Assessor’s supervision of personnel employed by his office and from transferring funds budgeted to his office. From the petition it appears that this is founded on the claim that the Board of County Commissioners set up an independent office to audit and review real property appraisal and assessment and have transferred personnel and funds levied for assessment purposes from the Assessor’s office without his consent or supervision. Immediately the question arises as to whether the Assessor had an alternative adequate and speedy remedy for these allegedly unlawful activities.1
Idaho Code § 7-402 embodies the common law rule that a writ of prohibition will issue only if no plain, speedy and adequate remedy at law is available. Cronan *754v. District Court, 15 Idaho 184, 96 P. 768 (1908); Little v. Broxon, 31 Idaho 303, 170 P. 918 (1918); Evans v. Court, 47 Idaho 267, 275 P. 99 (1929); State ex rel. Bank of Eagle v. Leonardson, 51 Idaho 646, 9 P.2d 1028 (1932). In Olden v. Paxton, 27 Idaho 597 at 601, 150 P. 40 (1915), this court cited with approval a Florida ease holding:
“It is a principle of universal application, and one which lies at the very foundation of the law of prohibition, that the jurisdiction is strictly confined to cases where no other remedy exists, and it is always a sufficient reason for withholding the writ that the party aggrieved has another and complete remedy at law. (High on Ex. Rem., sec. 770, and authorities cited.) And the writ will not be allowed to take the place of an appeal. In all cases, therefore, where the party has ample remedy by appeal from the order or judgment of the inferior court, prohibition will not lie, no such pressing necessity appearing in such cases as to warrant the interposition of this extraordinary remedy, and the writ not being one of absolute right, but resting largely in the sound discretion of the court.” Sherlock v. Mayor and City of Jacksonville, 17 Fla. 93 (1879).
In other cases, see Cronan v. District Court, supra, this court has emphasized that an appeal is normally an adequate remedy at law but that under some circumstances it may not be adequate and a writ of prohibition may therefore issue. E. g., Spivey v. District Court, 37 Idaho 774, 219 P. 203 (1923). But the burden is on the petitioner to show that his appeal remedy is inadequate. Smith v. Young, 71 Idaho 31, 225 P.2d 466 (1950).
The court finds no evidence in the record to show that petitioners made any attempt to appeal those actions of the County Commissioners of which they complain.2 Nor have they shown that appeals would be inadequate to redress their grievances. They have therefore failed in their burden of showing that no plain, speedy and adequate remedy at law is available. Idaho Code § 7-402 and a long line of Idaho cases prevent this court from granting the writ absent such a showing.
The application for the writ is denied. Order to issue.
BISTLINE, J., and COGSWELL, District Judge, concur.. The traditional common law remedy for an alleged usurpation of office is an action in the nature of quo warranto. I.C. §§ 6-602-6-609. Petitioners do not base their claim for relief on these provisions.
. The record is inadequate regarding the County’s alleged ongoing interference with the Assessor’s Office by way of diversion of funds and personnel. The record notes only that a “policy statement” was issued announcing such an intention. We do not know whether the “policy statement” was ever carried out. We do not know whether it was ever published or posted as an official “act, order, or proceeding of the Board” from which an appeal may be taken under I.C. § 31-1509. Nor do we know if any such appeal has ever been taken.