Geologist Drops Into the Dark to Put Light on San Clemente Slide : Bluffs: Two-foot-wide shaft is drilled 100 feet deep into La Ventana to examine the stability of hillside that gave way. Scientist descends to take a close look.

SAN CLEMENTE —  Working in conditions ideal for a mole, geologists descended 100 feet into a man-made hole Saturday to examine the stability of the ocean bluff that gave way last week, destroying five homes and dumping tons of rubble onto Pacific Coast Highway and the railroad tracks.

“We are evaluating the geology of the bedrock,” said Bill Goodman, a consulting geologist to the city of San Clemente.

Goodman, who works for Irvine-based Leighton & Associates, was caked with mud after spending an hour and 20 minutes underground.

He had been working in an open metal cage that was even narrower than the two-foot-wide hole drilled by a 40-foot-high rig into La Ventana, the street of pricey ocean-view homes, including those ruined by Monday’s massive landslide during heavy rains.

Wearing a helmet with a mining light to illuminate the darkness and relying on air pumped to him, Goodman used a knife and pick to scrape mud off walls in the hole to get a better look at the bedrock.

He used a two-way radio to relay information to a co-worker above on the street, who jotted Goodman’s observations in a notebook.

The conclusion?

“It really wasn’t very interesting,” said Goodman, meaning that he didn’t see any evidence of slippage at that spot on La Ventana, about 60 feet from the bluff’s edge.

But he hastened that “one hole doesn’t tell you too much. This point might be stable but a couple hundred feet down the street might not be.”

Goodman said the hole he explored Saturday is one of five the city of San Clemente will have contractors bore along a 600-foot stretch of La Ventana, beginning at the southern cul-de-sac and ending at Monte Vista.

Before the hole was refilled with concrete Saturday afternoon, a monitoring device was lowered into it that will alert geologists if the bluff starts sliding again.

The borings also are being explored by a geologist for the city of Dana Point. While the homes on La Ventana are within the city of San Clemente, the bluff and coast highway are within Dana Point.

Jules Darras, Dana Point’s geologist, said the city is most concerned about what steps it can safely take to reopen the coast highway. If more data is needed after the city’s work is completed on La Ventana, Darras said, Dana Point may drill additional holes into the bluff’s face.

According to Goodman, the Santa Fe Railroad, which owns the railroad tracks, has also hired its own geological consultant to determine whether debris can be safely removed from the tracks so Amtrak and freight service can resume.

The landslide has blocked railroad freight shipments from reaching San Diego County and Amtrak commuter service has been disrupted.