In Firestone Tire & Rubber Co. v. County of Monterey (1990) 223 Cal. App. 3d 382, the landowner was not "innocent" but the operator of a tire plant which, over the years, had been the site of enough spillage to prompt a pollution cleanup effort by the 1980's. But we must not forget that when it comes to the seemingly arcane world of property tax valuations, it is a Constitution we are expounding. Property tax valuations are governed by article XIII, section 1, subdivision (a) of the state Constitution, which requires all property to be assessed at "fair market value." (See also Firestone, supra, 223 Cal. App. 3d at p. 391.) The dispositive question is, therefore, always--as the Firestone court clearheadedly pointed out--not who has the liability for cleanup costs, but "whether, and to what extent, the property value was affected by the contamination." ( Firestone, supra, 223 Cal. App. 3d at p. 392.) The idea of innocence as the talisman for a reduction in a valuation assessment was properly rejected by the appellate court, albeit in dicta, in the Firestone case. Thus, even though the taxpayer lost the case on the ground that no potential purchaser would have been "aware of the contamination" as of the lien date for the property tax year in question (1980) (see 223 Cal. App. 3d at p. 395), the court still felt compelled, in its general statement of principles at the outset, to announce the proposition that " where the cost of pollution cleanup reduces the fair market value of property, it may form the basis for a reduction in that property's assessed valuation." ( Id. at p. 385.) Firestone is valuable for its dicta (see 223 Cal. App. 3d at pp. 390-393), because its actual holding is a rather prosaic one: The taxpayer did not show that the need to clean up the property existed as of the lien date. The key language as far as the actual holding case is found on page 395 of the opinion: "As of March 1, 1980, a potential purchaser would not have been aware of the contamination, the full extent of which, after its initial discovery in 1981, may not have been revealed until a few months before the April 1984 board meeting, and indeed, until much later still." Accordingly, the appellate court held that it was error for the trial court, as it had, to remand the assessment back to the appeals board for a reduction based on the "valuation for the 1980" tax year. ( Firestone, supra, 223 Cal. App. 3d at p. 385.)