ABANDONED. YA Book about girl who goes on Indiana Jones-style adventures

[Mina]

I remember reading these books where a teenage girl named Hesper went on Indiana Jones-style adventures with her guardian, who was an older man, perhaps an uncle. It was in the young adult section of the old library I went to as a teenager, so I assume it's YA. They were also at the beginning of the alphabet, because they were in the first section, so the author's last name probably starts with A or B.

[Jill]

Lloyd Alexander wrote the Vesper Holly series. Here's the first in the series:
https://www.goodreads.com/book/show/2...

[Abigail]

Vesper Holly would have been my guess, too.

[Lobstergirl, au gratin]

Mina, does that sound familiar?

[Lobstergirl, au gratin]

Lobstergirl wrote: "Mina, does that sound familiar?"

No response. Moving to Abandoned.