Seal Rocks is a bit of a misnomer, as the name arose from the Steller's and California sea lions who at one time hauled out on the rock. True seals are not known to have sat on these picturesque sandstone rocks jutting out of the sea just off the coast from the Cliff House. From the right angle you can even see an arch in one.
Lands End has been a long time in the making. Geologists have found the sandstone in the vicinity of Sutro Baths and the Cliff House to be 80 million years old. Radiometric dating of zircon crystals, a kind of mineral found in the sand, indicates that the grains came from an eroded ancient mountain range in Idaho. The zircon crystals from that range formed between 1 and 2 billion years ago were uplifted and eroded, then carried by a river from Idaho to Northern California around 80 million years ago. That river formed a large delta in the present Sacramento Valley and dumped sediment into a deep sea subduction trench in the San Francisco area.