Quicksilver (The Forensic Geology Series, Prequel) by Toni Dwiggins Page B

river. At least according to my grandfather’s letters, as interpreted by my father. The trail meets the waterway, at the southern grapes.”
    “Grapes?”
    “Early explorers found wild grapes growing along the banks and named the river for them. They spoke Spanish. Grapes in Spanish is uvas . My grandfather spoke Spanish. My father got a Spanish-English dictionary. Voila, the Yuba River. South fork.”
    “So from here,” I said, “Henry might go either direction.”
    Shelburne nodded. “Which way would you go?”
    ~ ~ ~
    W e had studied the geologic maps back at the lab.
    Out in the field, it was show time.
    The Shelburne family blue lead offshoot splintered at the river. There were mapped outcrops west, and east. So the question became, in which direction lay the contact metamorphic zone with the chiastolite hornfels aureole? Because that was the landmark Henry Shelburne would have sought.
    Walter spread his hands, east and west. “In either direction we have a pluton invading metamorphic rock. A pluton, if you’ll recall Mr. Shelburne, is a large body of igneous rock that can cook the country rock to hornfels.”
    “Good, fine.” Shelburne looked ready to bolt. “Which way?”
    I jerked a thumb downriver. “South Yuba Rivers Pluton is thataway.”
    Walter jerked a thumb upriver. “Bowman Lake Pluton is up yonder.”
    “Although,” I said, “we’re not necessarily looking for a large mapped pluton.”
    Walter nodded. “Could be a small and unmapped igneous dike.”
    “Which way do you like?” I asked my partner.
    Walter scratched his ear, considering. “I like the mapped rock unit up yonder.”
    As did I. The rock unit up yonder was known to have been intruded by numerous small igneous dikes. I said, “I tend to agree.”
    “Then let’s go.” Shelburne turned. “Upriver.”
    More like, above the river. The river was a good sixty feet below us.
    I paused to read a wooden interpretive sign staked into the ground. Once, the river had been level with the ground we now stood upon. And then debris had washed down from the mining pit above, elevating the river bed. And then, over time, the flowing water carved out its bed anew, leaving behind compacted-gravel benches like the one beneath our feet.
    As soon as possible we’d need access to the river.
    Meanwhile, we were at the mercy of the trail.
    Save for Shelburne occasionally shouting his brother’s name, we hiked in silence. It was a rollercoaster trail that took our breath away. The trail paralleled the river but the rugged rock of the canyon walls forced the route to climb, traversing the descending ridges and knife-gullied canyons. Now and again the trail dipped down steep rock benches to skirt the river but there was no way down to the gravel banks, save a dicey scramble.
    We pushed on.
    Finally we got lucky. The trail jacked hard right and switchbacked down to the river’s rocky bench.
    “What do you think?” Walter asked me.
    I took in the lay of the land. “I think it’s prime.”
    “I think,” Shelburne said, “we should keep moving.”
    Walter turned to Shelburne. “We need to establish a baseline. This appears to be a natural catch-basin for anything coming downriver. Sediment, debris, minerals. Including, perhaps, float from a metamorphic contact upriver.”
    Shelburne gave a brusque nod.
    I thought, something here doesn’t sit right with him. I wondered, what’s here?
    Nothing out of the ordinary, as far as I could see. The river bank was paved in cobbles and pebbles, armored with boulders. A gravelly sandbar extended halfway across the water.
    Shelburne sat on a boulder and folded his arms.
    Walter and I turned to our work. We shed backpacks and took out field kits. Walter claimed the rocky bank and I headed out on the gravel bar to sample the geology mid-river.
    I found a promising spot, a submerged bedrock hump that bridged the water and slowed its flow. A group of boulders gathered, forming deep crevices, a natural