James Edward Onisko

James Edward Onisko, known lovingly as Jim, passed away on May 31, 2025, at the age of 74. Born on December 19, 1950, in Ridgecrest, California, Jim lived a life filled with adventure, curiosity, and passion.

A dedicated drilling engineer, Jim worked for some of the world's largest operators, including Exxon and Marathon, making significant contributions to the industry. His expertise and dedication shaped his career, but his true joy was found beyond the office—in the great outdoors.

An avid cyclist, Jim spent many of his later years embracing the natural beauty of Colorado and South Dakota. His love for the open road and fresh air was a testament to his lifelong appreciation for nature. From his days as an Eagle Scout to earning his pilot’s license at a young age, Jim had an adventurous spirit that stayed with him throughout his life.

Jim is survived by his daughter, Michelle Grantham; his son-in-law, James Grantham; and their children, Austin, Abby, Emily, and Cole Grantham. He is also survived by his daughter, Katie Onisko and ex-wife, Jean Onisko. His presence in their lives was a source of wisdom, love, and encouragement, and his memory will be cherished always.

Jim’s journey through life was one of exploration, dedication, and heartfelt connection. His legacy lives on in the stories shared by family and friends, in the landscapes he cherished, and in the lessons he imparted to those who knew him best.