You could have done so 120 years ago. Mountain House was a 16-room hotel which opened in 1874, operating until 1895. John Muir described his visit in a letter of December 5th, 1877, to Dr. and Mrs. John Strentzel and Miss Strentzel. (Muir later married Louisa Strentzel, in 1880.) Muir’s visit is documented in The Life and Letters of John Muir in Two Volumes, published in 1924. There in he described a "capital little excursion over your Mount Diablo" when he spent the night at the summit:

"The sunrise was truly glorious. After lingering an hour or so, observing and feasting and making a few notes, I went down to that half-way hotel for breakfast. I was the only guest, while the family numbered four, well attired and intellectual looking persons, who for a time kept up a solemn, Quakerish silence which I tried in vain to break up. But at length all four began a hearty, spontaneous discussion upon the art of cat killing, solemnly and decently relating in turn all their experience in this delightful business in bygone time, embracing everything with grave fervor in the whole scale of cat, all the way up from sackfuls of purblind kittens to tigerish Toms. Then I knew that such knowledge was attainable only by intellectual New Englanders."

If you’d like to visit the site of the hotel (now unfortunately only marked by a State Park storage ground), follow the trail of the Old Stage Coach Road, located near the junction of North and South Gate Roads. A more complete description is given in the free MDIA brochure "Short, Pleasant Walks in Mt. Diablo State Park." Copies are available at the summit Visitor Center and throught MDIA's Store.

Also see Mountain House.