The author of this is better known (if known at all these days) as the author of the Mushroom Planet books. This is not anywhere as interesting: it's a realistic children's book (well, mostly realistic - there is a faint and feeble attempt to suggest some magic has occurred at the end); exactly the kind of thing a mid-century American librarian would approve of.
A young brother and sister are visiting their aunts at their Northern California mansion for Christmas. There they find the household in despair - Grandfather had died early in the year and to settle the estate, they had sold part of their land with redwoods - only to discover the purchaser is a sneaky evil developer who is going to chop down some of the redwoods on his new property to build housing and ruin the whole town! Oh no! There is one faint sliver of hope - the grandfather had written a new will before he died which left the redwoods to the state to create a park. If they could find that will before the end of the year, it would supersede the sale and save the land! (The family company is now doing better so they don't need the money after all.)
There are some nice descriptions of climbing along some cliffs on the California coastland, but otherwise, not much happens. The plot is ultimately resolved not by finding the will (turns out the grandfather tore that up) but by prompting a change of heart in the evil developer. Cameron tries to buttress this very unlikely resolution with some psychology (turns out he grew up in the area, played with the aunts as a child and the brother and sister give him a letter written by the developer's parents where they talk about how wonderful the trees are), but it's all very deus ex machina, and I think she realizes it, since in the last pages she adds the aforementioned suggestion of magic.
I read this as a child back in the early eighties, and the only thing I remembered about it was the fact they didn't find the will, which detail I quite liked. Other that that, very slight and forgettable.
