We are asked to determine whether a superior court can issue a constitutional writ of certiorari when a county makes a decision not to redesignate property from agricultural to commercial or industrial and the landowner does not exhaust all appeals. In this case, we conclude the superior court cannot, and reverse the decision of the lower court.
*785The controversy surrounds 25 acres of property zoned agricultural in King County, outside the Kent city limits, but inside Kent’s annexation area. The property had been zoned agricultural since 1941, but Torrance acquired the property in the 1960s in the hope of eventual industrial or commercial development.
In 1992, pursuant to the Growth Management Act (GMA), RCW 36.70A, King County designated the Torrance property agricultural lands of long-term commercial significance. The adoption of the comprehensive plan on November 18, 1994 did not change the property’s agricultural zoning, and Torrance did not appeal the designation.
In January 1995, King County enacted an ordinance adopting zoning, zoning maps, and development conditions to implement the 1994 comprehensive plan. Although still designated agricultural, the Torrance property received “P-suffix” zoning conditions. Under the terms of “P-suffix” conditions, the property retained its agricultural zoning, but the property-specific “P-suffix” zoning conditions allowed Torrance to use the property for “retail nursery operations, garden store, food gourmet stores, specialty food stores, university agricultural programs, restaurants, microbrewery and winery.” King County Ordinance No. 11653. Torrance did not challenge the application of the “P-suffix” zoning conditions to his property, but alleges he had no reason to do so because the permitted uses satisfied his needs.
The compatibility of “P-suffix” zoning conditions to the purposes of the GMA were challenged by other parties. In September 1995, the Central Puget Sound Growth Management Hearings Board (Board) held the “P-suffix” zoning conditions were not in compliance with the GMA. Clerk’s Papers at 146; see Alberg v. King County, No. 95-3-0041, 1995 WL 903142, at 15 (Central Puget Sound Growth Mgmt. Hr’gs Bd. Final Dec. and Order Sept. 13, 1995).1 In response to the Alberg decision, King County enacted *786Ordinance No. 12061 in December 1995, which removed the “P-suffix” conditions from the 1994 comprehensive plan and from the Torrance property. The removal of the “P-suffix” conditions did not alter the underlying agricultural zoning of the property, and Torrance did not appeal King County’s action.
In 1996, Torrance requested removal of the Torrance property from agricultural designation. This request was included in an amendment to proposed Ordinance No. 96-496 and would have rezoned the property from “the Agricultural Production district and Agriculture Land Use Designations to Industrial.” Clerk’s Papers at 147. The proposed amendments were considered, but were rejected and deleted before that ordinance was adopted because the King County Council decided not to change the property’s agricultural designation.
Torrance petitioned the Board to review King County’s decision not to reclassify the property. Clerk’s Papers at 124-25; see RCW 36.70A.280-.290. On March 31, 1997, the Board made two decisions. First, the Board determined Torrance was time barred from challenging King County’s agricultural designation of the property because more than 60 days had passed since the County’s 1994 and 1995 GMA actions. Second, the Board found King County in compliance with the GMA because the County’s decision not to adopt Torrance’s proposed amendments was not an illegal action under RCW 36.70A.130. Clerk’s Papers at 149-50. Despite the availability of judicial review in superior court, Torrance did not appeal the Board’s decision. See RCW 34.05.510; RCW 36.70A.300.
Instead, Torrance pursued a lawsuit filed December 13, 1996 (prior to the Board’s decision) in King County Superior Court. The lawsuit challenged King County’s 1996 decision not to adopt Torrance’s proposed amendments changing the agricultural designation of Torrance’s property. Torrance’s complaint included a cause of action under *787Washington’s Land Use Petition Act (LUPA), RCW 36.70C, arguing the decision not to adopt the proposed amendments was a land use decision subject to (1) judicial review; (2) a claim for damages under RCW 64.40; (3) a taking claim; and (4) a claim under 42 U.S.C. § 1983 for violation of Torrance’s constitutional right to substantive due process. Torrance later amended the complaint to include a request for a constitutional writ of certiorari.2
Following briefing and argument by the parties, the superior court determined the constitutional writ of certiorari would issue. The superior court found Torrance’s property was not agricultural land under the GMA and King County’s decision not to change the agricultural designation in 1996 was illegal. The superior court also found King County’s failure to change the designation of Torrance’s property following the Alberg decision arbitrary and capricious. The superior court ordered King County to adopt legislation changing the designation of Torrance’s property from agricultural to either commercial or industrial.
King County filed a petition for discretionary review of the superior court decision in the Court of Appeals. Torrance moved for transfer to this court. The motion was granted.
We must determine whether the superior court erred in granting the constitutional writ of certiorari. We review this issue de novo. Thomsen v. King County, 39 Wn. App. 505, 514-15, 694 P.2d 40 (1985) (appellate court should conduct de novo review of superior court’s writ decision).
A constitutional writ of certiorari is not a matter of right, but discretionary with the court. Saldin Sec., Inc. v. Snohomish County, 134 Wn.2d 288, 304, 949 P.2d 370 (1998). The law is well established that discretion can be exercised when no other adequate remedy at law is avail*788able and when the decision below is arbitrary, capricious, or contrary to law. Saldin Sec., 134 Wn.2d at 292-93; Williams v. Seattle Sch. Dist. No. 1, 97 Wn.2d 215, 221, 643 P.2d 426 (1982). If either a statutory writ of review or direct appeal of the decision is available, discretion to issue a constitutional writ of certiorari generally does not exist. Saldin Sec., 134 Wn.2d at 292-93.
The critical inquiry in this case is whether an adequate remedy at law existed and was available to the landowner. While many zoning decisions have been made in this case, for purposes of this opinion we examine whether the superior court can exercise its discretion and issue a constitutional writ of certiorari after the Board’s March 31, 1997 decision. To do so, we must examine what potential remedies were available to the landowner after the Board’s decision was made and determine whether the potential remedies provided the opportunity for adequate relief.
The GMA establishes an administrative review process designed to resolve allegations that a local government failed to comply with the GMA’s requirements. See RCW 36.70A.250-.345. The GMA requires that any person making such a challenge file a petition with a growth management hearings board (GMHB). RCW 36.70A.280.3 A petition for review must be filed within 60 days of the date the local government took the challenged action. RCW *78936.70A.290(2).4 The GMHB shall issue a final order finding the state agency, county, or city in compliance with the GMA, or not. RCW 36.70A.300.5 If a GMHB determines there is noncompliance, it shall remand the matter to the *790state agency, county, or city which must then correct the error and comply with the requirements of the GMA. RCW 36.70A.300(3).
Any aggrieved party may appeal a GMHB decision to superior court within 30 days of the final order of a GMHB. RCW 36.70A.300(5). A county zoning decision and a GMHB determination that the county’s decision was legal are decisions that may be appealed to superior court because compliance with GMA directives are involved. Washington’s Administrative Procedure Act (APA), RCW 34.05, governs judicial review of GMHB decisions, and the party asserting the invalidity of the agency decision carries the burden of proof. See generally RCW 36.70A; RCW 34.05.570(1)(a). A superior court can grant relief if the action substantially prejudiced the party appealing the GMHB’s decision. RCW 34.05.570(1)(d). Additionally, a superior court can also grant relief if: the order is in violation of a constitutional provision; the order is outside the statutory authority or jurisdiction of the agency; an agency engaged in an unlawful decision-making process or failed to follow its prescribed procedure; an agency has erroneously interpreted or applied the law; the order is not supported by the evidence; an agency has not decided all issues requiring resolution by the agency; a motion for disqualification was made and improperly denied; the order is inconsistent with a rule of *791the agency; or the order is arbitrary or capricious. RCW 34.05.570(3)(a)-(i).6 The writ of certiorari is unavailable unless the remedies available under RCW 34.05.570 are inadequate for full and complete relief. If an opportunity for full and complete relief is available, the general rule that the existence of a statutory appeals process bars a court from exercising discretion and issuing a constitutional writ of certiorari must apply.
We find that statutory review was available for Torrance to seek relief. In 1996, the King County Council decided not to adopt Torrance’s proposed amendments. The King County Council had the authority and jurisdiction to determine whether amendments or revisions to the comprehensive plan were necessary.7 As permitted by statute, Torrance sought review of the County Council’s deci*792sion by a GMHB. RCW 36.70A.280-.300. The Board determined it did not have jurisdiction to decide whether the 1994 or 1995 decisions complied with the GMA, but found King County had the authority not to adopt Torrance’s proposed amendments. Torrance did not wait to appeal the Board’s decision as permitted by RCW 36.70A.300(5), but chose instead to immediately proceed with a lawsuit filed December 13, 1996 in superior court (amended to include the constitutional writ of certiorari). The decision to forgo an available appeal and to instead seek a remedy by means of a constitutional writ of certiorari is fatal to Torrance’s case.8
*793Judicial review of a GMHB decision under RCW 36.70A.300(5) and RCW 34.05.570 provides an aggrieved party the opportunity for adequate and complete relief from a GMHB decision. In this case, an appeal of the Board’s decision to superior court would have provided Torrance with an opportunity to pursue the remedy he desired. Torrance argued the decision not to rezone the property was arbitrary, capricious, and illegal because, under the GMA, the property was not agricultural. Under the statutory appeals process, a superior court could provide a remedy if Torrance were correct. Torrance failed to avail himself to this process.
We hold the constitutional writ of certiorari is legally unavailable where a right to appeal exists and the failure to appeal is not excused. In this case, the superior court erroneously exercised its discretion by issuing the constitutional writ of certiorari because the opportunity for an adequate remedy was available and any final decision of a GMHB is appealable. Torrance’s excuse that an appeal was not necessary or required because the Board’s decision was not on the merits is incorrect. The only statutory requirement for appeal is that the Board’s decision be final, which the decision here was.
The superior court is not a zoning review superauthority permitted to substitute its judgment for that of the legislative authority under the guise of a constitutional writ of certiorari. Such a result is inconsistent with the purpose of the constitutional writ of certiorari. A writ of certiorari is an extraordinary remedy granted at the discretion of the court, but it is not available when a party has failed to *794avail itself to other procedures that would have afforded the opportunity for an adequate remedy. For these reasons, we reverse the decision of the superior court.
Durham, C.J., Dolliver, Smith, Guy, Madsen, and Talmadge, JJ., and Baker, J. Pro Tern., concur.
Torrance did not participate in the Alberg case because Torrance argues King County did not notify him the appeal was pending and because the Puget Sound *786Trust (plaintiffs in the Alberg case) did not join Torrance as an indispensable party.
The LUPA claims were dismissed by court order on April 24, 1997 because the superior court found King County took no action subject to challenge under LUPA. Torrance did not appeal the dismissal of the LUPA claims. Still pending in the superior court is a trial on damages Torrance may have suffered due to King County’s actions.
36.70A.280 (1996). Matters subject to board review.
“(1) A growth management hearings board shall hear and determine only those petitions alleging either:
“(a) That a state agency, county, or city planning under this chapter is not in compliance with the requirements of this chapter, chapter 90.58 RCW as it relates to the adoption of shoreline master programs or amendments thereto, or chapter 43.21C RCW as it relates to plans, development regulations, or amendments, adopted under RCW 36.70A.040 or chapter 90.58 RCW; . . .
“(2) A petition may be filed only by the state, a county or city that plans under this chapter, a person who has either appeared before the county or city regarding the matter on which a review is being requested or is certified by the governor within sixty days of filing the request with the board, or a person qualified pursuant to RCW 34.05.530.
“(3) For purposes of this section ‘person’ means any individual, partnership, corporation, association, governmental subdivision or unit thereof, or public or private organization or entity of any character.”
36.70A.290 (1996). Petitions to growth management hearings boards— Evidence.
“(1) All requests for review to a growth management hearings board shall be initiated by filing a petition that includes a detailed statement of issues presented for resolution by the hoard.
“(2) All petitions relating to whether or not an adopted comprehensive plan, development regulation, or permanent amendment thereto, is in compliance with the goals and requirements of this chapter or chapter 90.58 or 43.21C RCW must he filed within sixty days after publication by the legislative bodies of the county or city.
“(3) Unless the hoard dismisses the petition as frivolous or finds that the person filing the petition lacks standing, the board shall, within ten days of receipt of the petition, set a time for hearing the matter.
“(4) The board shall base its decision on the record developed by the city, county, or the state and supplemented with additional evidence if the board determines that such additional evidence would be necessary or of substantial assistance to the board in reaching its decision.
“(5) The board, shall consolidate, when appropriate, all petitions involving the review of the same comprehensive plan or the same development regulation or regulations.”
36.70A.300 (1996). Final orders.
“(1) The board shall issue a final order within one hundred eighty days of receipt of the petition for review, or, when multiple petitions are filed, within one hundred eighty days of receipt of the last petition that is consolidated. Such a final order shall be based exclusively on whether or not a state agency, county, or city is in compliance with the requirements of this chapter, chapter 90.58 RCW as it relates to adoption or amendment of shoreline master programs, or chapter 43.21C RCW as it relates to plans, development regulations, and amendments thereto, adopted under RCW 36.70A.040 or chapter 90.58 RCW In the final order, the board shall either: (a) Find that the state agency, county, or city is in compliance with the requirements of this chapter or chapter 90.58 RCW as it relates to the adoption or amendment of shoreline master programs; or (b) find that the state agency, county, or city is not in compliance with the requirements of this chapter or chapter 90.58 RCW as it relates to the adoption or amendment of shoreline master programs, in which case the board shall remand the matter to the affected state agency, county, or city and specify a reasonable time not in excess of one hundred eighty days within which the state agency, county, or city shall comply with the requirements of this chapter.
“(2) A finding of noncompliance and an order of remand shall not affect the validity of comprehensive plans and development regulations during the period of remand, unless the hoard’s final order also:
“(a) Includes a determination, supported by findings of fact and conclusions of law, that the continued validity of the plan or regulation would substantially interfere with the fulfillment of the goals of this chapter; and
*790“(b) Specifies the particular part or parts of the plan or regulation that are determined to be invalid, and the reasons for their invalidity.
“(3) A determination of invalidity shall:
“(a) Be prospective in effect and shall not extinguish rights that vested under state or local law before the date of the board’s order; and
“(b) Subject any development application that would otherwise vest after the date of the board’s order to the local ordinance or resolution that both is enacted in response to the order of remand and determined by the board pursuant to RCW 36.70A.330 to comply with the requirements of this chapter.
“(4) If the ordinance that adopts a plan or development regulation under this chapter includes a savings clause intended to revive prior policies or regulations in the event the new plan or regulations are determined to be invalid, the board shall determine under subsection (2) of this section whether the prior policies or regulations are valid during the period of remand.
“(5) Any party aggrieved by a final decision of the hearings board may appeal the decision to superior court as provided in RCW 34.05.514 or 36.01.050 within thirty days of the final order of the board.”
RCW 34.05.570(3) (1996). “Review of agency orders in adjudicative proceedings. The court shall grant relief from an agency order in an adjudicative proceeding only if it determines that:
“(a) The order, or the statute or rule on which the order is based, is in violation of constitutional provisions on its face or as applied;
“(b) The order is outside the statutory authority or jurisdiction of the agency conferred by any provision of law;
“(c) The agency has engaged in unlawful procedure or decision-making process, or has failed to follow a prescribed procedure;
“(d) The agency has erroneously interpreted or applied the law;
“(e) The order is not supported by evidence that is substantial when viewed in light of the whole record before the court, which includes the agency record for judicial review, supplemented by any additional evidence received by the court under this chapter;
“(f) The agency has not decided all issues requiring resolution by the agency;
“(g) A motion for disqualification under RCW 34.05.425 or 34.12.050 was made and was improperly denied or, if no motion was made, facts are shown to support the grant of such a motion that were not known and were not reasonably discoverable by the challenging party at the appropriate time for making such a motion;
“(h) The order is inconsistent with a rule of the agency unless the agency explains the inconsistency by stating facts and reasons to demonstrate a rational basis for inconsistency; or
“(i) The order is arbitrary or capricious.”
RCW 36.70A.130 (1996): “Comprehensive plans—Amendments.
“(1) Each comprehensive land use plan and development regulations shall be subject to continuing evaluation and review by the county or city that adopted them.
*792“Any amendment or revision to a comprehensive land use plan shall conform to this chapter, and any change to development regulations shall be consistent with and implement the comprehensive plan.
“(2) (a) Each county and city shall establish and broadly disseminate to the public a public participation program identifying procedures whereby proposed amendments or revisions of the comprehensive plan are considered by the governing body of the county or city no more frequently than once every year except that amendments may be considered more frequently under the following circumstances:
“(i) The initial adoption of a subarea plan; and
“(ii) The adoption or amendment of a shoreline master program under the procedures set forth in chapter 90.58 RCW
“(b) All proposals shall be considered by the governing body concurrently so the cumulative effect of the various proposals can be ascertained. However, after appropriate public participation a county or city may adopt amendments or revisions to its comprehensive plan that conform with this chapter whenever an emergency exists or to resolve an appeal of a comprehensive plan filed with a growth management hearings board or with the court.
“(3) Each county that designates urban growth areas under RCW 36.70A.110 shall review, at least every ten years, its designated urban growth area or areas, and the densities permitted within both the incorporated and unincorporated portions of each urban growth area. In conjunction with this review by the counly, each city located within an urban growth area shall review the densities permitted within its boundaries, and the extent to which the urban growth occurring within the county has located within each city and the unincorporated portions of the urban growth areas. The county comprehensive plan designating urban growth areas, and the densities permitted in the urban growth areas by the comprehensive plans of the county and each city located within the urban growth areas, shall be revised to accommodate the urban growth projected to occur in the county for the succeeding twenty-year period.”
At oral argument Torrance argued an appeal under RCW 36.70A.300(5) was not required because the March 31, 1997 Board decision was not on the merits. This argument fails because the only requirement for appealing a decision under RCW 36.70A.300(5) is that the decision be a final decision of a GMHB. The *793March 31, 1997 Board decision is titled, ORDER GRANTING DISPOSITIVE MOTION, and states, in part:
“Based upon a review of the petition for review, the briefs of the parties, the RCWs, the Board’s Rules of Practice and Procedure and prior decisions of this Board and the courts, the Board enters the following ORDER:
Respondent King County’s motion to dismiss is granted; Torrance’s petition for review (Case No. 96-3-0038) is dismissed with, prejudice. The Hearing on the Merits, scheduled in the Notice of Hearing in this matter, is canceled.
So ORDERED this 31st day of March, 1997.” We find the Board’s decision constitutes a final decision subject to appeal. Clerk’s Papers at 150.