This dispute arose between plaintiffs, the owners of property on a portion of the Oregon Coast known as “Big Whale Cove,” and defendants, the owners of adjacent property to the north on which “Little Whale Cove” is situated, over whether each had access to the other’s cove.1
Plaintiffs brought this lawsuit seeking to quiet title against defendants’ claim of a prescriptive easement over a trail on plaintiffs’ land that runs south from Little Whale *482Cove to Big Whale Cove, and requesting a declaratory judgment that their property includes a portion of the “dry-sand area” of Little Whale Cove, giving them access to the entire “dry-sand area” of Little Whale Cove under Thornton v. Hay, 254 Or 584, 462 P2d 671 (1969). Defendants asserted, as a counterclaim, their right to the prescriptive easement to Big Whale Cove. The state intervened to assert the public’s right to use the “dry-sand area” of Little Whale Cove and to enjoin defendants from interfering with that right. No party claimed public access from land to Little Whale Cove.2
*482The trial court ruled against defendants on their counterclaim. Concerning plaintiffs’ and the state’s claims, the trial court held that the beach at Little Whale Cove does not contain “dry-sand area” subject to public recreational use under Thornton v. Hay, supra. The trial judge concluded that the pool at Little Whale Cove
“is not part of the ocean. It is a fresh-water pool occasionally influenced by the Pacific Ocean. The dry sand area is a beach abutting the pool, situated entirely on private land. The beach is not dry sand area along the Pacific Shore open to the public for recreational use.”
The court also held that, in any event, any “dry-sand area” of Little Whale Cove lies to the north of the boundary line between plaintiffs’ and defendants’ property, negating plaintiffs’ claim of access.
Plaintiffs and the state appeal.3 Both argue that the trial court erred in ruling that Little Whale Cove does not contain “dry-sand area” along the Pacific shore subject to the rule in Thornton v. Hay, supra. Plaintiffs also argue that the trial judge erred in holding that plaintiffs’ land does not contain any of the “dry-sand area” of Little Whale Cove. The underlying action is in equity and, therefore, we review de novo. ORS 19.125; Rogelis v. Pettis, 49 Or App 537, 539, 619 P2d 1339 (1980), rev den 290 Or 449 (1981); Lindsay v. Dairyland Insurance Co., 278 Or 681, 688, 565 P2d 744 (1977).
Little Whale Cove is a small, coastal inlet, located about five miles south of the city of Depoe Bay. The mouth of *483the cove lies between two rocky points directly to the north and south. The cove rises from the ocean over a sloping rocky foreshore up to a flat sill where it opens into a tidal pool surrounded by a narrow beach. The beach, in turn, rises to steeply-sloped sandstone cliffs and upland vegetation. Two small freshwater streams flow into the tidal pool from the east. The rocky points and the sill at the westward edge of the cove are of basalt and are covered at or near the water level with barnacles, mussels and various forms of marine algae. The tidal pool has a smooth, sandstone bottom which slopes upward to the beach from a depth of about seven feet at the base of the sill. The tidal pool is about 150 feet wide from the inside edge of the sill to the beach.
Testimony, as well as numerous exhibits, indicate that the fan-shaped configuration of the cove results from a constant pattern of wave action entering the narrow opening at its mouth.4 The bottom of the cove is scoured clean in most places by wave action and in sheltered areas exhibits a rippled texture in sediments deposited by the waves. The steeply sloped berm at the edge of the pool was formed by wave action. The waves deposit kelp, seaweed and driftwood on the beach and at the base of the cliffs on either side of the pool forming a “strand line.”
The beach itself is composed of coarse grains of basaltic matter and small snail shells, sea urchin spines, broken clam shells and other debris from coastal animals. Fragments of mussel shells are also found on the beach. These materials are washed onto the beach from the ocean.
Mean high tide lies seaward of the cove’s mouth, about 50 feet from the inside edge of the sill. Ocean waves do not reach the interior of the cove during low tides. However, the two small streams at the east end of the cove continue to trickle water into the pool, keeping the water level at the lip of the sill. The result is a stratification of the water in the pool, *484with the lighter freshwater lying on the surface of the pool and the heavier saltwater from the ocean settling on the bottom. During high tides, the ocean waves wash back into the pool, increasing the salinity.
A variety of marine plants and animals inhabits the cove. The craggy sill is covered with red and green algae, intermixed with small intertidal organisms. Inside the pool live marine snails, mussels, hermit crabs, shore crabs and an abundance of shrimp-like crustaceans. They are marine organisms and cannot survive continuous exposure to fresh water.
A line of vegetation is visible on the upper boundary of the beach above the tidal pool. Experts at trial characterized this “upland” vegetation as typical of coastal areas in the Pacific Northwest. The vegetation nearest the beach consists primarily of silverweed, which is a perennial plant that becomes dormant in late fall or winter, although its extensive root system survives and sends up new shoots in the spring. During winter or when exposed to ocean waves, the tops of silverweed turn brown. The plants may be carried away by waves “sufficient to move the beach.” The amount and color of silverweed visible on the ground on the south side of Little Whale Cove fluctuate seasonally. Landward from the beach, the silverweed becomes mixed with other upland species of vegetation including sea rocket, grasses, thistle, Queen Anne’s lace, rushes, horsetails and, ultimately, willows and Douglas fir. Between the visible line of vegetation and the mean high tide line, there is no vegetation of any other freshwater upland species.
There are two issues: 1) Whether Little Whale Cove contains “dry-sand area” that is subject to the public’s right of recreational use under Thornton v. Hay, supra, and 2) whether a portion of any “dry-sand area” at Little Whale Cove is located on plaintiffs’ property.
In Thornton v. Hay, supra, the Supreme Court determined the rights of the public in Oregon’s shoreline. The court held that “ocean-front lands from the northern to the southern border of the state ought to be treated uniformly.” 254 Or at 595. Applying the English doctrine of custom, the court held that the “dry-sand area” along the shore “has been used by the public as public recreational land according to an unbroken custom running back in time as long as the land has *485been inhabited” and the public had acquired an easement for recreational purposes between the mean high tide line and the visible line of vegetation. 254 Or at 595; see also State Highway Commission v. Fultz, 261 Or 289, 292, 491 P2d 1171 (1972).
The evidence shows that Little Whale Cove is part of the ocean shore created by the Pacific Ocean and that the beach at Little Whale Cove lies between the mean high tide line and the visible line of vegetation. Surveyors for both the state and defendants plotted the mean high tide line just outside the mouth of the cove, 50 feet from the inside edge of the flat, rock sill. Every witness who testified on the subject identified the silverweed growth line as the seaward edge of the upland vegetation. The tidal pool and the beach at Little Whale Cove lie between the mean high tide line and the visible upland vegetation. Therefore, we hold that Little Whale Cove contains “dry-sand area” within the meaning of Thornton v. Hay, supra, which is subject to the public’s right of recreational use as a matter of law.5
Defendants argue, and the trial court found, that, because the beach in this case does not “abut” mean high tide, but is separated from mean high tide by a basaltic sill and a tidal pool, Thornton v. Hay, supra, does not apply. Defendants contend that, because Little Whale Cove’s unique geographic characteristics “separate” its beach from mean high tide, it is not subject to the public’s right of use. That is the sort of tract-by-tract analysis that the Supreme Court sought to avoid. The court employed the term “dry-sand area” to designate that part of the ocean shore between the mean high tide line and the visible upland vegetation line (also known as the back-shore). It did not limit its ruling literally to dry sand. 254 Or at 595.
Whether a particular parcel of the coast is made of fine sand, coarse pebbles or solid rock is irrelevant to a determination whether it is “dry-sand area.” Similarly, the frequency with which a beach is washed by ocean waves is of no *486consequence, if the beach lies between the lines of mean high tide and visible vegetation. If that were not so, the public’s use of Oregon’s beaches would depend upon complex presentations of biological, botanical and geomorphological data specific to each and every beach, cove and inlet on the coast.6 The result, inevitably, would be a patchwork quilt of coastal lands, some subject to public use and others not, with no clear means available to the using public to tell which is which. The proper question for the trial court was whether the beach at Little Whale Cove is situated between the lines of mean high tide and visible vegetation.7 The evidence shows that this beach is so situated.
Defendants argue that applying Thornton v. Hay, supra to their cove results in a taking of property without just compensation and due process of law in violation of the Fifth and Fourteenth Amendments to the United States Constitution and Article I, sections 10 and 18, of the Oregon Constitution.
There is no merit in defendants’ due process argument.8 Defendants contend that Thornton v. Hay, supra, applies only to the particular beach at issue in that case and that its application without a beach-specific determination of public customary use denies them due process. In Thornton, the Supreme Court merely confirmed the public’s right of use in the “dry-sand area” of Oregon’s beach land, which the public has always assumed to be a part of the public beach. Although the “dry-sand area” belongs to the property owners, it has always been subject to the public’s recreational easement. Application of Thornton does not violate defendants’ *487due process rights.9
Defendants also fail to establish the primary element for a “taking” claim, that is, a protected property interest.10 State law is the source of the sticks that constitute a property owner’s bundle of rights. Ruckelshaus v. Monsanto Co., 467 US 986, 1001, 104 S Ct 2862, 81 L Ed 2d 815 (1984). Thornton v. Hay, supra, 254 Or at 589-90, made it clear that any title to ocean shore land between the lines of mean high tide and visible vegetation has historically been encumbered with the public’s recreational easement. See also State Highway Commission v. Fultz, supra, 261 Or at 292. The court in Thornton stressed that the “dry-sand area” along the ocean shore is sui generis. It said:
“While the foreshore is ‘owned’ by the state[11], and the upland *488is ‘owned’ by the patentee or record-title holder, neither can be said to ‘own’ the full bundle of rights normally connoted by the term ‘estate in fee simple.’ 1 Powell, Real Property § 163, at 661 (1949).” 254 Or at 591.
The court found that for as long as there has been an institutionalized system of land tenure in Oregon the public has freely exercised the right to use the “dry-sand area” on the whole Oregon coast for recreational purposes. 254 Or at 596. It further found that
“the custom of the inhabitants of Oregon and of visitors in the state to use the dry sand as a public recreation area is so notorious that notice of the custom on the part of persons buying land along the shore must be presumed.” 254 Or at 598.
Thus, the court in Thornton merely declared a right of use which the public has always had:
“The rule in this case, based upon custom, is salutary in confirming a public right, and at the same time it takes from no man anything which he has had a legitimate reason to regard as exclusively his.” 254 Or at 599.
Defendants have no protected property interest in the public’s easement over the “dry-sand area,”12 and therefore there can be no “taking.”13
*489Finally, defendants argue that the state is barred from asserting the public’s right of recreational use in the “dry-sand area,” because defendants have a “reasonable investment-backed expectancy of exclusive use of Little Whale Cove.” The state characterizes this argument as claiming estoppel against the state. Defendants fail to make a case under either theory.
The facts giving rise to defendants’ argument are that, in 1971, defendant Halvorson asked the Oregon Department of Justice whether the state had any interest in Little Whale Cove. At that time, Halvorson was considering purchase of Little Whale Cove. A deputy attorney general advised Halvorson in a letter that the state currently had no interest. That conclusion was explicitly based on the wrong premise that “the property has no sandy beach because of a high basaltic cliff arising directly up from the ocean.” Halvorson admitted that the deputy told him that the state’s legal position with regard to Little Whale Cove could change. As a result of the deputy’s advice, Halvorson claims, he invested more money in developing Little Whale Cove than he would have if the state had claimed an interest. Because Halvorson knew that the conclusion was based on erroneous facts and that the state’s position might change, there is no estoppel.
In support of their argument, defendants rely primarily on Kaiser Aetna v. United States, 444 US 164, 100 S Ct 383, 62 L Ed 2d 332 (1979), a federal “taking” case, where the Supreme Court held that Hawaiian law had created a private property interest in Hawaiian fishponds. 444 US at 166-67. Private owners of a fishpond known as Kuapa Pond (a shallow lagoon separated from Maunalua Bay by the Pacific Ocean and a barrier beach) invested substantial amounts of money to create a boat access between the fishpond and the ocean on the basis of advice from the Corps of Engineers that no permits for the development or operation of the pond were needed. The federal government then asserted a navigational servitude over the pond. The Court held that, if the government wished to make what was formerly a private fishpond into a public aquatic park after petitioners had gone as far as they had, it could not require them to allow the public free access without paying just compensation. 444 US at 180. In that case, as well as in the other federal cases cited by defendants, state law had created a protected property interest. *490Here, however, defendants have no protected property interest in the public’s easement over the “dry-sand area.” Therefore, as a matter of law, defendants cannot have an investment-backed expectancy.
Halvorson testified that, if he had known of the public’s right to use the cove, he would have developed the site as larger parcels rather than as an urbanized development. The mere fact that money has been invested in a particular level of development does not transform this case into a Kaiser Aetna taking. A mere unilateral expectation is not a property interest entitled to protection. Webb’s Fabulous Pharmacies, Inc. v. Beckwith, 449 US 155, 161, 101 S Ct 446, 66 L Ed 2d 358 (1980).
We now turn to the issue of whether plaintiffs’ property includes any portion of the “dry-sand area.” That depends upon whether the visible line of vegetation is north or south of plaintiffs’ property line.14
Thornton v. Hay, supra, describes the vegetation line as “the seaward edge of vegetation where the upland supports vegetation.” 254 Or at 586. The court noted that the vegetation line remains “relatively fixed,” while the western edge of the “dry-sand area” is subject to dramatic moves eastward or westward in response to erosion and accretion. 254 Or at 589. The trial court found the property line involved here
“to be south of the permanent natural vegetation line; that is, the line is landward of the * * * ‘dry sand’ area surrounding Little Whale Cove.
“* * * [T]he actual boundary line is south of or at least in the grassy area and it is not on the beach. Consequently, I find that the plaintiffs have no access to the dry sand area surrounding Little Whale Cove.”
Plaintiffs do not contest the trial court’s characterization of the visible line of vegetation as the “permanent natural vegetation line.”15 They argue, however, that the evidence shows *491the property line to be north of that line, at least when the silverweed turns brown or is washed away by winter waves.
We find that the vegetation line at Little Whale Cove remains relatively fixed, although the color may change. Moreover, the overwhelming weight of evidence shows that, regardless of where the vegetation may be located at any given time, the vegetation line remains north of the property line. Photographs in evidence and expert testimony presenting a detailed survey of the species of vegetation found within Little Whale Cove and their location placed the property line in the zone of vegetation where the silverweed becomes mixed with grasses and herbs (“meadow species”), about 40 feet south of the seaward edge of vegetation as it is marked by the silver-weed. Thus, there is no “dry-sand area” of Little Whale Cove on plaintiffs’ property. Plaintiffs’ claim of access is defeated.
We reverse the trial court’s ruling that Little Whale Cove does not contain “dry-sand area” subject to the public’s right of recreational use and remand for entry of an appropriate judgment; we affirm its ruling that the plaintiffs’ property does not include any of the “dry-sand area” of Little Whale Cove.
Reversed as to intervenor’s claim and remanded for entry of judgment for intervenor; otherwise affirmed.