“She was almost unknown then, so I was able to spend a lot of time shooting her,” Clark recalled. After all, it was still early in her career, and she’d only just begun to gain attention: Three months before this shoot, she appeared as a crooked lawyer’s girlfriend in The Asphalt Jungle; two months later, she had a small role as an aspiring starlet in All About Eve.

“We’d go out to Griffith Park [in Los Angeles] and she’d read poetry. I sent several rolls to LIFE in New York, but they wired back, ‘Who the hell is Marilyn Monroe?’” (Three years later, Marilyn appeared on the cover of LIFE in a now-famous Clark photo, posing with her Gentlemen Prefer Blondes co-star, Jane Russell.)

Clark’s pictures of Marilyn offer a rare glimpse into the early days of an eventual pop-culture icon’s career, when a young actress was blissfully unaware of what the coming years would bring and was, it seems, just happy to be in “the industry” and getting noticed. LIFE magazine, however, never published the gold mine of photos seen in this gallery after Marilyn became a bona fide superstar. Whatever the reason, one thing remains perfectly clear: at 24 years old, in 1950, Marilyn Monroe was already something special.