Quoted:
Im not a native, but I thought all the Denny regrade material went Belltown & north. I didnt think it came to Pioneer Square area.
AFAIK, Pioneer Square is "natural" grade.
View Quote
I could be wrong. My recollection from all of the MOHAI visits and underground Seattle tours is pretty close to the WIki depiction below. My understanding was the Hill was in the area you described, but it was used to fill south west of the original location, all the way to the water. Everything that is pioneer square and waterfront area was much lower before the regrade. I laugh to think of whether or not a project could even happen like this today. Listen to this one.Using water pumped out of lake union (flooding) to take the top of the mountain off and letting the water run downhill to Elliot Bay. Environmentalist's heads would explode like the opening scene to the movie Scanners.
The Denny Regrade project was the removal of Denny Hill, one of the proverbial seven hills of Seattle. It ran east from First Avenue between Pike Street and Denny Way. Hill and street were named after the Denny family, who were among the city's earliest white inhabitants. The First Avenue regrade was started in 1897 and completed on January 6, 1899. From 1902 to 1911, the hill was sluiced into Elliott Bay by pumping water from Lake Union using hydraulic mining techniques, in a series of regrades along Pike and Pine Streets, Second Avenue, and the massive Denny Regrade No. 1 which regraded everything remaining between Fifth Avenue and the waterfront. In 1929–30, Denny Regrade No. 2 removed the final pieces of the hill east of Fifth Avenue using steam shovels.
From the Pioneer Square Wiki
https://en.wikipedia.org/wiki/Pioneer_Square,_Seattle
Early history
The settlement's importance was guaranteed in 1852, when Henry Yesler chose the site for his lumber mill, which was located on Elliott Bay at the foot of what is now Yesler Way, right on the border between the land claimed (and soon thereafter platted) by David Swinson "Doc" Maynard (to the south) and that platted by Arthur Denny and Carson Boren.
Much of the neighborhood is on landfill: in pioneer times, the area roughly between First and Second Avenue, bounded on the south by Jackson Street, and extending north almost to Yesler Way (about two-and-a-half city blocks) was a low-lying offshore island. The mainland shore roughly followed what is now Yesler Way to about Fourth Avenue, then ran southeast, at an angle of about 45 degrees to the current shoreline. Slightly inland were steep bluffs, which were largely smoothed away by regrading in the late 19th and early 20th century