Carl Sagan, in his very popular (1980) TV series, "Cosmos," showed pictures of "The pyramids of Elysium" taken by the Mariner 9 mapping of Mars in 1972. This picture is reproduced on page 129 of his book, Cosmos ; and on page 130 he has the following footnote about these Elysium pyramids:
"The largest are 3 kilometers across at the base, and 1 kilometer high -- much larger than the pyramids of Sumer, Egypt or Mexico on Earth. They seem eroded and ancient, and are, perhaps, only small mountains, sandblasted for ages. But they warrant, I think, a careful look." [Sagan] .