dissenting in part.

The majority relies on Community Redevelopment Agency v. Aetna Casualty and Surety Co., 50 Cal.App.4th 329 , 57 Cal.Rptr.2d 755 (Ct.App.1996), for the proposition that the insured must exhaust the limits of the underlying primary policies for all the years during which a continuing loss occurred, but Community Redevelopment does not go quite so far. Community Redevelopment was not a case about policy limits; it was about a duty to defend. As Community Redevelopment explains, under Montrose Chemical Corp. v. Admiral Insurance Co., 10 Cal.4th 645 , 42 Cal.Rptr.2d 324 , 913 P.2d 878 (Cal. 1995), primary insurers in successive years may, indeed, be hable for contributing to the common defense of a continuing tort claim that spans several policy years. See Community Redevelopment, 57 Cal.Rptr.2d at 761 . This is so because it is unclear at the beginning of the lawsuit which portion of a continuing claim will be covered by any particular policy; it is sufficient that a claim be arguably covered by a policy for the duty to defend to kick in.

Our question is quite different: Does the excess insurer for a particular year avoid liability on a claim arising during a year when the primary policy limits are reached, because the primary limits are not reached in subsequent or prior years? In my view, the answer is no; if the primary policy is exhausted in a particular year, the secondary insurer is hable for the excess, and the existence of primary insurance in other years is not relevant.

Even though a loss may be continuing, it does not follow that it will be homogeneously distributed throughout the period in question. There may be larger losses in earher years and smaller losses in later years, or vice versa. Because the exact contours of the liability distribution are not known when the lawsuit is brought, the duty to defend apphes to ah primary insurers within the period of continuing loss. But, once the claims are adjudicated, we know how the losses are allocated and we can tell whether the primary’s limits are reached in each policy year. If the primary limits are reached and exceeded for a particular year, no further primary insurance is available for that year and the secondary becomes liable for the excess. This the risk it’s been paid to assume.

To illustrate by example, assume six successive primary policies of $1 million each, covering six successive policy years. Also assume excess insurance of $2 million for each of those years. There is a continuing loss and claims are presented for a total of $5 million. Because, under Mont-rose, each of the primaries may wind up being liable for a portion of the $5 million loss, they must each contribute to the common defense of those claims. At the same time, none of the excess insurers is required to contribute, so long as the primary contribution limits remain unexhausted. That’s what Community Redevelopment holds, and I have no quarrel with it.

But the situation looks quite different after the claims are adjudicated. Assume that, although the loss is continuing, it varies in magnitude over time, so that most of it occurs in the early years, and much smaller portions in the later years. Thus, the losses are distributed as follows: *854 year one, $2.5 million; year two, $1.5 million; year three, $500,000; year four, $250,000; year five, $150,000; year six, $100,000. In this situation, I see no reason to hold that the excess insurer in year one is off the hook, even though the loss that year far exceeded the limit on the underlying primary policy for that year. Rather, I would hold that the excess insurers in the first two years are liable for $1.5 million and $500,000, respectively. I am aware of no California case that holds to the contrary and I am most reluctant to conclude, as does the majority, that the California courts, if confronted with this situation, would hold that “California law requires horizontal exhaustion before an excess insurer is required to defend or indemnify its insured.” Maj. Op. at 852 (emphasis added).

In our case, Lafarge and Travelers negotiated a global settlement for an amount less than the.aggregate policy limits on the underlying primaries. The settlement allocated the loss non-homogeneously throughout the period. Specifically, for 1970, it allocated $500,000, which exhausted the per occurrence property damage limit for 1970. I agree that Appalachian is not bound by this allocation, which may have been collusive. But the allocation does present a prima facie case of liability for the excess insurer in 1970. If the excess insurer disputes the allocation, it is entitled to present evidence that the allocation does not reflect actual losses during the year in question. But this is a matter of proof, and cannot be won by the excess insurer on summary judgment.

Therefore, while I agree with the majority that Appalachian should be entitled to prove that some of the underlying primary coverage is not collectible, I would also remand for consideration of the proper allocation of losses for the various years during the period of the continuing loss.